I have Daylite which I used fairly often at my last job. Daylite is just a little too much for my current job and it is still not as linked to iCal and Addressbook as I would like.
Ran across
this the other day and it looks interesting. Kinda makes me think of what the user center for Office 2004 is. Except it uses the AddressBook, Mail and iCal as it's database.
Anyone tried it?