free ideas i have that are just floating through my head, warning value of these ideas may vary. dramatically. 
1. (already discussed elsewhere) What if both uncle ben and aunt may had both been killed, Spider-man grows up to be a villain - who can stop him?
 
2. (removed this idea for being crappy after re-reading it)
 
3. Alternative Banshee from X-men story. Banshee and his brother Black Tom Cassidy are mutants in the IRA. Banshee can use his voice to set off a sonic boom which deafens anyone in the area and causes blackouts and Black Tom can turn wood into a lethal weapon. The story set in the 70s sees the two irish men travel over to London as part of a terrorist plot. Banshee naively believes the target of the attack is the British Military, when he finds out that Tom is actually planning to attack a tourist hot spot, Banshee must decide what sort of man he wishes to be. Rebelling against his brother, Tom is caught and Banshee returns to  Ireland. While there Banshee marries the girl that both brothers had fought over before. Tom returns setting up a mighty battle but what neither irishmen know is that Tom was followed by the first British super-soldier - UnionJack. A racist englishman who hates the Irish, with the ability to track the men across the country. The two brothers must try to escape the soldier before they can settle their own score. 
 
4. X-men story, Cyclops gets Emma Frost preggers. he sets out to hand the leadership role over to one of the x-men but which one? And in Shi'ar space the find out that another Summers child is on the way and set out to stop it (cos you know, shi'ar believe that summers kids are always vessels for the phoenix force...) Oh and if Emma turns diamond this could hurt the baby... so her defenses are low
 
5. Another x-men related story, while in Shi'ar Space, Cassandra Nova telepathically enslaved a commoner and commanded it to clone her cells with the cells of Lillandra to create a daughter for her. This child is half human-half Shi'ar. Named Lilandra Nova (yeah i like it too) this girl has it out for the x-men, especially Emma Frost. this could easily tie into number 4.  
 
6. Alternative future where Batman and Superman are both dead and the earth is almost fully enslaved by Kryptonians with only a few rebels. these rebels include Dick Grayson still operating as Robin (or redrobin i like that costume) and Supergirl, (in this world superman's daughter) and a seemingly reformed Lex Luthor. Also a one armed green arrow. The rebels attempt to travel back in time before Doomsday killed Superman. As events unfold only Supergirl and robin travel back. This leads them to confront Bats, Supes and a young robin. But it also shows that Lex luthor really was evil - so what changed? At this time it appears that Lex luthor was communicating with kryptonians in space (pirate kryptonians of course who were never on krypton when it 'sploded) and he tries to bring them to earth to use them to overthrow the world and become the ruler. However the Kryptonians dont want to serve luthor so luthor makes a kryptonian hybrid - one that can survive kryptonian radiation - dubbed "Doomsday". The present and future characters have to race against time to stop the future from happening again! 
 
7. Cyclops from the early days of the x-men (just pre-phoenix saga) is transported into the future where he finds Wolverine now running the x-men. Cyclops immediately tries to overthrow wolverine believing that wolvie must have done something suspicious to future cyclops. Cyclops easily defeats the old wolverine and humiliates him thus usurping him as leader of the x-men. Wolverine admits that in this time, he has lost most of his healing power and is slowly aging. Cyclops begins to discover that the future ... isnt that perfect.... and that wolverine isnt his real enemy
 
8. Alternative green lantern, Hal Jordan is an average man until the bright light hits him and turns him into a prophet for an interstellar religion called the Green Light. The light grants him  a ring to help humanity discover the power of the religion. Hal develops his own religion dedicated to teaching the world about Justice and Equality and a new method of living that just might save humanity. The only problem is that the world thinks he's nuts. Including the worlds other messiah - superman.  
 
 
9. Sentry pre-dark reign.  
Bob reynolds is the sentry but he has forgotten his past. Trying to pick up the pieces with his wife Lindy, he tries to reconnect with the people he saved. He finds a website dedicated to him that retains information that failed to get wiped out when the Sentry was repressing himself. He tries to meet the people who have left messages on the website but ... they are all dead. Except for one woman and her son who are still alive. Somehow, Sentry knows that this is the work of the Void. He believes that the void is killing off every person he ever saved and that this woman is next. obsessively he watches over the woman and child like a pagan god watching over a small tribe. Although initially uncomfortable the woman begins to relax around the Sentry as the boy takes a liking to him. This does not sit well with Lindy who begins to wonder why Bob is spending so much time with them. before things get too Jerry Maguire the sentry sleeps with the woman, the void shows up and tries to kill the mom and son. Sentry fights with him but the void launches an attack on the son. The son defends himself with a bright light shield. The sentry is convinced that this power is similar to his own. The void flees realising that leaving the woman alive will cause more problems for sentry and Lindy. Sentry tries to figure out what the boy is but the woman seems unusually defensive about him suddenly. Sentry is convinced that the boy is in fact his own son. In a panic he kidnaps the kid and takes him to the Baxter building. Reed reluctantly agrees to test the DNA but warns Sentry that this could ruin his marriage to Lindy, Bob gets frustrated with reed and tells him that he doesn't appreciate his family enough and that Bob has always wanted kids more than anything. Reed retorts that only a month ago this would never have been on his mind.  The results show that the boy's DNA is similar to Bobs. But the possibility that Bob gave the boy powers to make him feel like a son is also possible. Sentry confused (as usual) returns the child to his mother and pretends that the test conclusively shows that he is the father in order to trick her into a confession. the woman says that she will take bob to the court if he tries to make a deal out of this as super heroes families are walking targets. Sentry out of shame and depression agrees to this. In the final scene he is sitting on the roof of the watch tower. The void appears sitting beside him. Instead of launching into a battle the two discuss who the void is, the sentry noticing that the void's timing is too good to be true. The void admits that he isn't real and that the Sentry keeps bringing him back not to complicate his life but to simplify it. "When I'm not around, you have to deal with your own actions." Void says "But when I am out there killing - you can simply escape into your own fantasy where you are the only one who can save the day." The Sentry sits silently looking out into the evening sky. He has no answer. "Want to fight about it?" the void says with a grin.  
"Yes." 
 
10. Alternative world again, Batman versus superman. Batman and Superman have agreed to set up a team for superheroes to make sure they are raised with the correct values. Superman begins recruiting Flash and Wonderwoman etc. but Batman remains out of it, prefering to be a silent partner. Clark becomes upset with Bruce and argues with him over this, Bruce agrees to help out more if Clark will let Wayne Industries experiment on his spaceship. Clark reluctantly agrees. Bruce meanwhile is forming his own team this one with only humans - Dick Grayson, Jason Todd, Tim Drake, Oliver Queen and Dinah (whatever black canary's name is) to be Batmen and to take down super people should they Become corrupt. The spaceship deal goes sour and the world blames superman who in turn blames bruce/batman. This leads to an epic fight of epicness. Jason Todd dying along the way to motivate batman like a good ol' refrigerator death cause that always helps make the fights epic.    

Out of all of these I love the 3rd one. Sound brilliant and gritty.... Something Ennis should write. 

Elseworlds are for DC Comics. Marvel Comics uses What If's.