We've used
www.greekgear.com and
www.greeknation.com.
www.thegreekshop.com is good too but they are slow as all get-out.
I might also suggest for T-shirts, etc. maybe finding a local embroidery or greek-clothing related store in town. Sometimes they'll work with you on getting things like your crest or other graphics into a format to be printed. Good luck!