WhatsApp Messenger is a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for iPhone, BlackBerry, Android and Nokia and yes, those phones can all message each other! Because WhatsApp Messenger uses the same internet data plan that you use for email and web browsing, there is no cost to message and stay in touch with your friends.
2. Tone Picker
Use Tone Picker to set MP3s for SMS, IM, Email, Ringtone, Notification, Alarms, Calendar, whatever.Use any builtin tone or MP3 Has volume sliders and quick-set ringtone and notification.
3. GTunes Music Lite
A simple interface to search, download and play millions of free and legal quality MP3 music on public domains . Download MP3 with this and make it a ringtone with TonePicker..
4. FLV Player -->
not awesome but a nice way to be able to watch .flv type movies
5. K-9 Mail -->
As nb_mitch states..nothing to add to his/her comment..
nice app to sync files through your computers and phone.. even sharing folders with your friends via shared folder options.. 2 gb comes as free.. AWESOME
7. SetDNS -->
Good for reaching blocked web-sites..
8. Fringe -->
As DellStreakLuv states..Also I want to mention the capability of being able to chat with Iphone users..I still couldnt get Skype to work and Fringe is an awesome help on this issue
9-10. Games --> AngryBirds, SliceIT
5 Stars for AppBrain (as nb_mitch states)