I can't think of any like MTurk, but there are a lot of freelance writing sites. If you're into writing, you might want to check out your options. I don't know if it is against TOS to mention any, but I use to write for Demand Studios before they went downhill. :/ You can try checking it out and apply to specific sections. There is also Hubpages for a passive income - I get about $100/month there. You can also try blogging for money from AdSense.
I signed up for clickworker.com a long time ago, but there never seems to be any work available for me.
You can also try oDesk but you will have to be more proactive about writing cover letters, applying for jobs, making yourself look like a good candidate.
app.payperpost.com pays well, but the work is extremely intermittent. They also require you to maintain your own blog, they have a 30 day approval window and a 30 day payment window. I have never had someone take all 30 days to approve, but the payment window is locked to exactly 30 days; perhaps down to the second. I like it, but again, results and work are highly variable. There is also a $2.00 penalty for transferring funds out for amounts under $50.00. Textbrokers.com is the reverse of the above. You submit a writing sample and they rate you from level 1-5. The fifth level requires a test, which is a beast. The problem with this site is you are given a topic and have to meet goals, yet are paid by your skill level established at the start or gained through steady improvement. This causes issues of expectation. For example, some will ask for a detailed company press release, in less than 500 words and require level 3 ranking and the requester rejects 90% of everything they receive. What they are really looking for is a professional writer (level 5) to work for .01 a word. The other issue is the mixing of levels; at level 4, I can do tasks for levels 1-4 and swipe away tasks from lower level people. The problem I have with this is that the only way to gain levels is to do more tasks (or test high as I did from the start). I have done one job on this site. I am looking for an opportunity to do more, but mturk has stolen away my drive. (How was this for a first post?)
Believe me there is nothing like mturk and no site can be matched to mturk as per my online earning experience. I will suggest one site if you PM me.
Slicethepie looks pretty interesting. How have you been liking it and what's your experience with getting the pay?
Whatever you do, DON'T use shorttask!!! Those sheisty mf's STILL owe me $13.00 for a single task I did on their site TWO YEARS AGO. At first, they said they had some "technical issue with PayPal, and that they would transfer my money as soon as it was resolved." After that, they stopped responding to my emails, and no matter what I've done, I cannot get a response from them as to where my money is. Needless to say, I've posted negative things about their company all over the net, Ripoffreport, and the scam sites. Don't mess with them. Most of their tasks would violate mTurk TOS, and in fact, the owner of shorttask was banned from mTurk for violating TOS, so he created his own site. The tasks are scammy and spammy, often requiring one to sign up with a website, or some such. Most importantly, YOU WON'T GET PAID!
I just joined a few days ago so haven't been paid yet. I haven't really used it very much yet. I think you get paid through Paypal and can cash out at $10.