Fearless Formula Feeder is my fav blog for formula-feeding moms. It's helped me tremendously to overcome guilt about quitting breastfeeding, and the author is non-judgmental and non-preachy about breastfeeding as well as formula-feeding.

Today, she started a series called "The FFF Quick-and-Dirty Guide to Formula Feeding" and starts off with a guide to mixing bottles: http://www.fearlessformulafeeder.com/2011/10/fff-quick-and-dirty-guide-to-formula.html

There's tons of great info in this post as well as the rest of her blog, so please go take a look!