My favorites are HubPages and Yahoo Contributor Network.
YCN has a slightly lower payout (~$2 CPM compared to ~$3 CPM here), but the domain tends to have greater strength. All things equal, an article at YCN would probably rank higher than an article here at HubPages. At least, that's my experience.
But YCN also involves more up front editing, and you have less control as a writer to edit and adjust your work. It's a great place to publish works where you've already done your keyword research and determined how to target keywords in search engines, where-as HubPages gives you more flexibility to change things at will and experiment until you hit just the right combination of words.
But by far my biggest earner is my private blog. I earn about $30 to $40 / month on YCN, $10 (soon to be more) on HubPages, and way more than that on a blog that I completely control and monetize through AdSense and Amazon Associates.