I switched to CM Eclair ROM recently and am forced to live without the Sense UI. Here's my list of must have android apps (the order is not significant):
Dialer One - The best Sense dialer replacement.
Dropbox - I have it on all my internet connected devices.
Meebo IM - Used for facebook chat.
SyncMyPix - Sync contacts with facebook
Facebook for Android
988 Pomocnik - Serbian CallerID
TV Vodic - TV Guide, Serbian version
Calling Flip - flip to phone while ringing to turn of the ringtone.
In-app Wifi Toggle - turn on wifi from any app