Heck, I’d go so far as saying if you have any iPhone, unlock it, get a decent data plan and a last.fm account, and install MobileScrobbler. It’s that good.
This app is what the default "iTunes" app on the iPhone should do. It provides advanced information on the current track you are listening to, including artist bios, lyrics, upcoming artist events, tags, similar artists, etc.
If you’re into music sharing, you can have MobileScrobbler "scrobble" the tracks up to last.fm as you listen to them. As an example, here’s my profile, showing the tracks I have listened to (on random shuffle most of the day).
Depending on your data plan, you can also stream music from last.fm. Using your preferences and played tracks, last.fm will create a custom playlist of similar styles and artists for you.
MobileScrobbler is well built, and completely integrated into the iPhone experience. Somehow they’ve even added a widget to the system setting screen so it seems like a system extension.
This is simply the best iPhone/iPod Touch app I have come across.