Ends today at 10PM PT. Shirt.woot! is offering 40% off $15 or more orders. Discount will be auto-applied at checkout. Shipping is free for Prime members. They have tons and tons of geeky and pop culture designs. Check out Top 20 Designs and Bestselling Designs. 

Also, here are several ongoing sales this week:

• Gearhead Shirts
• Shirts to Call for a Good Time
• Serious Shirts!
• Shirts to Add to the Closet
• Music Shirts
• Shirts Fit for Royalty