Have looked for some of the apps listed above - seems a number of them aren't available here. In any case, not a top ten below, but perhaps some that are of use:
Shazam - free song recognition app. [Using microphone.] Also provides additional information and links relating to the songs you find. Have used it enough times to identify relatively obscure music - even at a distance - to say that it is essential.
Tunein Radio - largest international directory of stations that I've been able to use. International blocking introduced by one US company a few months ago meant my own access to some of my favoured news / sports stations was removed, but it shouldn't be an issue for anyone in the US. Also allows recording and playback of previous shows depending on the station.
eBuddy Pro - instant messenger app. I find it has better functionality than the windows live app, which is the only other one I would consider using. Some may prefer Beejive.
Justin.tv - free. Watch streams on justin.tv. Works surprisingly well, and in my case, often better than when using a computer. Broadcast function is apparently forthcoming for the new iPod Touch in the next update.
NHL Ice Time - entirely dependent on level of interest, of course, but this allows me to watch highlights and listen to games that might otherwise be blocked via standard radio apps. Waiting for new release.
Picture Safe - manage locked photo albums and videos [with additional bought update].
Worms - Classic game. Disturbingly addictive.
Google Earth