Demandstudiossucks.com

I've had good luck with the following sites:

www.freelancewritinggigs.com - This site used to be owned by Deb Ng, but she sold it late last year. They post leads every weekday. Occasionally an affiliate link or scam sneaks through, but for the most part the leads are solid, non-content mill leads

www.online-writing-jobs.com - Updated daily. I have the best luck checking late Sunday night, before the regular weekday people find the ads. I've picked up quite a few private clients and solid gigs from this board. I'd be wary of sending unpaid samples, as there are some scammers about, unless you have a few that you send over and over. I usually link to a LS article or two for samples.

Freelance Writing Gigs is quite awesome. I've applied for so many different gigs through there. Most don't reply but usually a few do and I can weed out the good ones.

Media Bistro is good to. You can sign up and just have them email you when anything comes up in the field you want. I got one of my current jobs through there and at least it's a step up from trying to crank out how-to articles for DS.

And then of course there is the lazy way to do it, which is to search "write for us" (with the quotation marks) in Google. It pulls a ton of sites that accept freelance submissions.