I suggest if you want really good mobile internet, get a Touch. MobileSafari is the best mobile browser I've ever used - it's not slow (like the NDS) and it's actually capable of rendering web pages without screwing them up (like the PSP). If you need to zoom in on an area, it intelligently zooms in on the area on a double tap. The only thing missing on it is Flash support (which is rumoured to be coming soon). If you jailbreak it you can install email, google maps, vnc, and tons of other apps. I have a 16GB and I have some music, the first season of Flight of the Concords, Transformers, Harry Potter and the Order f the Phoenix, The Simpsons Movie, a lot video/audio podcast and 2 pages of apps.
If you want tons of music and video, get a regular iPod.