Amen to the search suggestion. There's a lot here already!
In my opinion, AIM on the BlackBerry ain't that great. Built in client is SMS, which is possibly costly and definitely sluggish. Ramble I have found to be unreliable, and the others I have found to be non-free, which makes me not interested. So I stick with Google Talk, and I LOVE it. The GoogleTalk/AIM integration piece doesn't appeal to me because I don't want to bother with keeping a dedicated desktop logged in to support it.
http://www.bigblueball.com/forums/go...msn-yahoo.html
http://google.com/gmm for awesome maps. This is an absolutely killer application.
Google Maps is all I need, and I travel a lot. But it doesn't do GPS. For that check out
www.telenav.com.
I make my own ringtones from my MP3 and sound effects collection, saved as 48Kbps mono MP3 files, hosted in a private area of my web site. All the sounds my BlackBerry makes are custom tones I've cooked up in this way. TMI?
Games?
www.magmic.com -- something for everybody there.
eBooks?
www.mobipocket.com -- can import your own content from a variety of formats.
Good luck and have fun! If you want to go deeper, look into "Zen Theme" -- you'll need to get your hands a little dirty, but most people who try the Zen theme really dig it.