As others are suggesting, Crowdflower works, and works well, with an excellent API. Also they are just good people. (They use an assortment of workforces)
For smaller jobs self service jobs like the one described in this article SmartSheet UI is amazing. http://www.smartsheet.com/ (MTurk based)
And if you need bigger stuff (or text oriented stuff), with some consulting you can contact me, or my company http://castingwords.com (MTurk based)
How do you plan to accept payments? How much would Houdini itself cost (per task, per month?)? Do you plan to accept non-US users?
Pricing is still TBD. MTurk charges will be passed through directly to you with Houdini-specific charges either per task or per month.
Yeah, I'm planning on accepting non-US users.