I have quite a few apps installed, and a few favorite apps (dialer one, handcent, astro, overclock widget) but one of my favorite, most used and downright awesome apps I've found has to be dropbox!
I can download a song that catches my ear on amazon (or a free mp3 app ) , upload it to my dropbox and instantly have it on all my desktops and mobile devices that have dropbox on them.
If I'm working on an important document (such as university papers), drag and drop the file straight to my dropbox on my laptop, and instantly have it with me everywhere I go, and have it backed up very safely.
Anybody else just in LOVE with dropbox ?
**by the way, in case you want to try dropbox http://db.tt/WDgwXDG is my referral, you normally start off with 2gb, but if you use a referral link you get an extra 256mb to start off with (and so do I)