Greekclothing/greekave..... you know, and this is no exaggeration, they have the best prices and the best turnaround. I got a crapload of gifts for some APO neos last spring and everything arrived on time and good quality.
I mainly will stick with them if I just need letters and no shields/crests or other more complicated stuff.
I like the combo packages at
http://greeknation.com/
http://www.joetoga.com/ and
http://www.collegecrib.com/ are my favorites for just plain GIFTS (not clothing)
http://www.greekgear.com/ has great specials sometimes too. I like them for screen printed shirts
Finally,
http://www.thegreekshop.com/mtolympus.html for crossing jackets and the like.