2 days ago, kindle for android was finally released. I downloaded it and it immediately synced with all my purchased books, right down to the page I am on, with my kindle. That's a nice feature.
I had kindle on my iphone, and actually like reading on my phone better than on my kindle. (With my vision, I need the backlighting). So with a bigger brighter screen, it will really be nice.
Love Grocery IQ, it does so much for a free app. It's best feature may be how it syncs with my husband's phone, so whatever he adds to the list shows up on my list, and whatever I add also shows on his. Same for when one of us purchases something and checks it off the list.
TikL Touch-to-Talk: this walkie-talkie app seems to be glitchy for some, but works fine between our phones, and is very handy.
Tunee, for free music.
No-Lock for getting rid of the lock screen and being able to use the volume buttons to turn the phone on.
Lookout for easy data backup, anti-virus and phone finder.
I have many of the others that have been mentioned, but these are some I thought I'd hit on as having found very useful.