Here's NCSU's Craig Newmark:
A Lifehacker poll ranks Allrecipes.com first.
The rest of the list is, in order as ranked by LifeHacker readers: Epicurious, Food.com, SuperCook, and Bing Recipe Search. Here's the comment I left on Craig's post complete (now with embedded links!).
I use Allrecipes all the time. But I also like to watch Chef John's video recipes at foodwishes.com . He has good recipes and entertaining videos. I have learned lots of useful techniques by watching him and Diners, Drive-ins, and Dives which is also good for coming up with creative ideas for recipes.
As I've gotten more experience in home cooking, I've gotten a better feel for something my mom used to do. She used to not use measuring spoons/cups etc, instead relying on her eyes and tastebuds. But I countered that it's at least important to write down one's own recipes so that they can be passed down.
Anyways, one of the things I like about Chef John's videos is that in addition to the recipes, it is useful to watch him assemble a dish to get a feel for time-saving (and clean-up avoiding) techniques.