Garbage Can/DumpsterObviously, in Gotham City, there are tons of garbage cans and dumpsters laying around, and times when you may feel as though you're just dropping in on people way too much, jumping out of a pile or trash, covered in banana peels, is just as effective/scary as hanging off a randomly placed gargoyle. Although this may be very effective, it's quite smelly and it may take weeks to get the smell of week old Chinese food/diapers out of the BatSuit.
Lying Under A CarIt's all about the execution. First, he'd have to find a car tall enough to slip under easily, but not so tall that it will blow his cover. He would really have to make sure that he A. laid on his back, so his belt doesn't scrape on the ground and B. wait for the thug to say something like, "no one will ever stop us!" That's when Batman would strike. As cool as it may be to slip from underneath a car, Batman really has to do a lot of wiggling, which is neither that tough nor sneaky.
Piggy-Back RideThis is the true test of how sneaky Batman can be: Hines Ward sneaky. As with the rest of these places Batman could hide, I've never seen him hide on a thugs back, but I know it can happen: He's just that darn good. Little does Mr. Thug know that while he's been planning the crime of the century, Batman has been listening to the whole thing, and taking notes, while riding on his back.... Epic. Is this possible though? Well, either it's going to be the biggest failure at stopping crime in the history of super-heroes, or Batman will fail miserably. There is no middle ground.
Effectiveness: Either 1/10 or 10/10
Hot Air BalloonBruce Wayne (What? You thought I was talking about Dick Grayson? No sir! Bruce is much sneakier/ninja-like) has millions of millions of dollars, and on top of that, he loves taking ladies out for a night on the town. What do ladies love more than anything else? Hot air balloon rides. Science fact. So, how can billionaire Bruce Wayne utilize his romantic piece of transportation at night? By jumping out of it onto the bad guys. The only thing he'd have to watch out for is flying too low because then the possible villain could hear the flames shooting into the balloon. Otherwise, this is a perfect way to help Batman hide from the villains.
Pizza Delivery GuyLaugh it up, but how effective would it be? IMMENSELY! A bunch of criminals meeting in their local thuggery, planning the next "big score," and the pizza guy shows up. The thugs pay the man for the pizza, and BOOM! POW! SNEAK ATTACK! They were never expecting Batman to be the pizza guy, were they? Heck no! I'm sure after the 8th-15th pizza, the bad guys would catch on, but then they'd probably order from Pizza Hut instead of Domino's, and Batman would catch on quickly and just switch uniforms. This is the most effective of all the hiding spot theories I have, as long as Batman has a direct connection to everyone ordering a pizza and every pizza shop in Gotham. Seem impossible? Yes, but he's the G.D. Batman!
These are all incredibly plausible, but what place do you think Batman hides in before he jumps on the bad guys?