Not sure if alot of people will be interested in this but here goes.
Gamegoldonly : very friendly, often available on msn, smooth transaction , 8$/1000g currently for EU gold.
Gametradeking : friendly, always on MSN, fast payment (by e-gold) , 8$/1000g for EU gold
THsale : very friendly support, 0.01$ / g for EU atm, only if your server is in demand.
Offgamers : Updated several times a day (offgamers.com/buyback.php , click US or EU) , very prompt payments.
Mogs.com : 12$ / 1000g, cant test them myself cuz i dont play a US server but read below.
If i come any other sites i will post them here. Hope this helped some people