Essential Ant-Man Vol 1
Collecting the earlier adventures of the tiny-hero from Tales to Astonish. This book contains key moments from Hank Pym's life like his first Giant-Man appearance and the first appearance of The Wasp! By Stan Lee and Jack Kirby.
Avengers Vol.1 #28
First appearance of Hank Pym as Goliath.
Avengers Vol.1 #59-60
First appearance of Yellowjacket the man who killed Hank Pym and his wedding with The Wasp!
The Mighty Avengers #21-36
These 16 issues serve as a character study for Pym and chronicle his adventures as Wasp II to honor his late wife Janet by leading a new team of Avengers through the events of Dark Reign and Siege. Also featured is Dr. Pym being named Scientist Supreme by Eternity.
Spinning out of The Mighty Avengers following the events of Siege, This 39 issue series sees Pym unite with other former Avengers such as Quicksilver, Tigra, and Jocastato create a school where the next generation of Earth's Mightiest Heroes can be trained by the best of Earth's Mightiest Heroes.
Age of Ultron #10AI
This issue provides a good insight into the history of Hank Pym, and also sets the groundwork for a new status quo for the character.
Probably the easiest way to jump into the character in current continuity without having to break the bank, this series features a Marvel Now! Hank Pym as he leads a team of Avengers against A.I threats such as Dimitrios, the sentient Iron Man armor.
Avengers: Rage of Ultron
This Marvel graphic novel is possibly one of the greatest Hank Pym stories of all time. The story features the Avengers fight Ulton who has taken over the moon Titan. The story is loads of fun and features the biggest status quo change in the history of the character. For those interested, the change is that Hank Pym and Ultron fuse together to become a cyborg Ultron at the end. Although the story may be deemed out of continuity following Secret Wars, it is still a fun read and I recommend it