I know, I know its been done to death but who here doesn't love when video games involve inflation.
Here is a list of some games I haven't seen listed here before:
Eternal Darkness (Gamecube). Personally haven't seen it myself, however through many sources I have been informed there is a breast expansion "Easter egg" involving the main female character. Props to someone who finds/knows of this
Haunting Grounds (PS2) A resident evil type game which features a female lead. Using an Action Replay you can increase her bust size by 4 sizes. Big, Bigger, Huge and DAMN!
Example:http://www.youtube.com/watch?v=WHpSdbIbKTw
Dig Dug Arrangement/Namco Virtual Arcade (360-iPhone/iPod) The classic Dig Dug game, only remade with all new animations, power ups and bosses that need to be inflated to huge sizes before popping. Picked up my copy for 12$. Well worth it.
Example:http://www.youtube.com/watch?v=X-It3Sn1aa0
Timesplitters:Future Perfect (Xbox/PS2/GC?) Some might know of this FPS game. It involves a gun called the "Injector Gun" which inflates your enemies with each dart fired into them. 2 darts and they expand and then burst damaging everything in their area.
I have more typed out on a document, just to tired at the moment to search. Feel free to add some more games or titles.
Super Mario Galaxy 2 had a new item called "blimp berry" that inflates Yoshi and allows you float up higher to reach higher places.