Depends what type of thing you're after I guess but the obvious one is Baris Manco who did loads of stuff mainly in a prog/psych/funk style.
There are a load of his records listed here on popsike
http://www.popsike.com/php/quicksearch.php?searchtext=baris+manco
Only got a few singles of his myself but the one everyone is after is 2023.
Other people to look out for include Okay Temiz (crazy jazz), Orhan Gencebay (kind of like Serge Gainsbourg from what I've heard), Senay (done some fuzzy psych tunes).
Finders Keepers have just re-issued an album by Selda
http://www.finderskeepersrecords.com/discog_selda.html
And this thing which sounds wicked from the soundclips
http://www.finderskeepersrecords.com/discog_mustafa.html
There are loads of others in psych prog type styles such as Mogollar, Ersen, Uc Hur El etc but again I've only got singles by these and I couldn't really tell you what the best bits are.
A lot of people are buying Turkish records at the moment and people seem to have cottoned on to this and started flogging everything they've got on ebay so one of the best ways to find out about this stuff is search there because a lot of them put up sound files.