This is a list of twitter clients for osx available on the mac app store.

1) twitter official client
pros
works with lists
multiple accounts
looks excellent

cons
can only view one thing at a time, eg you cant have a live stream of two accounts at once
no sync support

2) tweetdeck
pros
works with lists
multiple accounts
can view multiple live streams concurrently

cons
looks rubbish
no sync support

3) janetter for twitter
pros
works with lists
multiple accounts
can view multiple live streams concurrently
theme support

cons
no sync support

4) echofon lite for twitter
pros
works with lists
multiple accounts
can only view one thing at a time, eg you cant have a live stream of two accounts at once
syncs between iphone and mac so you dont read the same tweets again and again

cons
ad supported, there is a paid version available though