Check this thread. Also check places like discounttiredirect.com, 1010tires.com, tirerack.com. Visit local tire shops or places like the Costco Tire Centre. Sometimes shops run promos like buy 3 tires, get one free, or places like Costco offer rebate programs. Tire manufacturers may also run a periodical rebate program.
I would suggest figuring out your budget, deciding what is most important to you in a tire, then shopping online and locally to find the best deal.