It's a small savings (just $5), but if you shop at Costco anyway, they look to have the best price on Windows 7 upgrades that we've seen yet.
As we reported earlier, retail pricing puts the Windows 7 Home Premium upgrade at $50 with the Windows 7 Professional upgrade costing $100. Costco will give you $5 savings on each, putting Home Premium at $45 and Pro at $95. That's a 10% savings on Home Premium and a 5% savings on Pro...or about enough to take a healthy bite out of sales tax. [Costco Thanks Brian!]
UPDATE: They pulled the page we linked and jacked up the price. Lame.