The only wrong answer is 50/50: Calculating the co-founder equity split http://www.geekwire.com/2011/wrong-answer-5050-calculating-cofounder-equity-split/
Foundrs Calculator http://foundrs.com/
The Founders Pie Calculator method http://www.andrew.cmu.edu/user/fd0n/35%20Founders%27%20Pie%20Calculator.htm
How much a non-technical co-founder should receive? http://blog.nahurst.com/how-much-equity-a-technical-cofounder-should
High Tech Startup Valuation Estimator (More for fundraising, but good things to think about) http://www.caycon.com/valuation.php