you can have all the apps in the app store and it probably wouldnt take up even 3GB. 8gb is a lot of memory. so dont worry about memory capacity with an iphone.
Apps don't take up that much space. Most are about 2-5 mb. Theres 1024 mb in one gb. Some good games are tap tap, t4two, and cube runner. Other ones are nytimes, facebook, myspace, remote, yelp, and aim.
The ones I have are Weather Bug, Paralingo, aurora feint, tap tap revenge, break classic, remote, facebook, aol radio, bubbles, currency, scribble, and tris (basically tetris)