to be fair any airsoft site will have a decent range of budget dots for you. unless your after something specific we cant really say anymore on the matter.
The Trijicon MRO clones are OK, as are most of the 551/552/553 types. The cheaper ones... Well, they're cheap, but generally they'll all do the job for Airsoft.
As a rule be wary of the ones that offer a selection of reticules. The couple I've had don't seem to hold their zero very well.
What samurai said, for repro red dots the best kind is the T-1 type. The small lens means you suffer less from parallax and the tube type sights are much more resilient.
Okay thanks guys, I've gone with a WE 882 holo sight for now, the build I've got now was always gonna be a budget build, it's when I get my nuprol honey badger it's only going to be the best stuff going on.