It really depends on how much you make (what tax bracket you are in) and how many deduction you claim. On average it seems that about 20% - 25% of your paycheck goes to taxes. Check out the link below, it lets your put all your info in and it calculates how much will withheld.
Social Security tax for 2011 is 4.2%, Medicare is 1.45%. Depending on which state you live, depends on whether you pay state disability or other local taxes. As far as federal or state income tax, irs.gov has tables you can check and your state should too.