These are the other sites that I've come across in my searches. I haven't worked for any of these (unless otherwise specified) so my assessments are rather brief and superficial. If anyone would like to add any experiences with any of these companies please make a comment.
ShortTask. Another click-to-work site but unfortunately not one of the better ones. The problem lies in the work available, which is mostly from SEO operators asking you to submit links or other similar activity. These tasks are actually banned under mechanical turk for example. The trouble with these tasks is that, apart from having to engage in dubious activity (for example making multiple posts to craigslist), they are simply not suitable for repetition and hence not suitable for accruing any substantial reward. Until they get a wider range of and tidy up the work they offer I will not be using this site myself. Payment is made to PayPal accounts, and can be requested whenever your balance exceeds $10.
Microworkers, our final site suffers from the same problem as ShortTask, specifically the type of work on offer. Again it mostly consists of tasks like "sign up to my forum", or "post a comment" etc., which unfortunately take too much time for the pennies that are on offer. Payments can be made in amounts of $9 or greater in a number of methods including PayPal, but can take up to a month to be processed. On the positive side, they do credit you a dollar when you sign up.
Another site that seems to deal in small SEO type tasks. This seems very similar to the Microworkers in the sort of work they process. They even also have a one dollar sign up bonus as well.