Can anyone give me some advice on making a good chess club shirt or a good site to make cheap custom shirts? I have a simple design planned out, but am thinking of adding a good line like the one on the Chess.com shirt.

Try cafepress.com.  And btw there are some nice chess shirts at ebay:

http://clothing.search.ebay.com/chess_Clothing-Shoes-Accessories_W0QQ_trksidZm37Q2el1313QQfromZR40QQsacatZ11450

CafePress or Zazzle are my recommendations.

CafePress is what Chess.com uses.

thanks, I'm most likely going with cafepress, it's a LOT cheaper than anywhere I've checked...