Shazam - Music ID
Twidroid - They have a paid version and a free one... the new update they did is pretty nice... it makes twitter an enjoyable experience :-)
Ringdroid - Make ringtones from your phone using any music stored on your phone
iMusic - Allows you to download music to your phone...
Handcent - SMS client that lets you customize your fonts, colors, etc
ChompSMS - Another SMS client that lets you customize