Reeder for RSS, even if you don't use an RSS feed reader now, if you read the same websites regularly, you may as well.
Total finder, finder with tabs and some extra features but the most important thing is that it retains the general interface of finder. I don't know about you but I use finder a lot so even the smallest of things help.
Sparrow, just a very good email client.
Coversutra, if you create music, I'm guessing you listen to a lot as well. I find the search feature to be very useful and better than Bowtie's (free) for my usage style.