Thwipster has already found success with its great deals on comics (I would already have made taken advantage of them multiple times if I didn’t have Amazon Prime). But now they’re expanding into the collectibles market, with deals on statues, toys, and other geek-oriented merchandise.
Figure of the Day doesn’t have quite the profile of Thwipster yet, but they have had some excellent deals. They’ve also had a few “theme days,” when they sell a number of figures from the same franchise–e.g., Predators or G.I. Joe–over the course of a day. Thwipster charges $3 for shipping while FOTD’s shipping is free.
In general, Thwipster appears to have slightly higher-end/higher quality merchandise on the whole, while FOTD tends to be a bit more of a crapshoot from day to day–sometimes the figure is awesome, sometimes it’s obviously a retailer trying to unload remainder stock.
However, they’re both worth checking up on every day, because you never know what you’re goind to find.
On a side note, the Groupon comparison isn’t quite accurate, as Groupon deals represent an assurance contract whereby if enough people sign up, then the sale goes through; but if too few people sign up, it doesn’t happen. That doesn’t seem to be how Thwipster and FOTD work–they seem to offer straight daily deals on a particular collectible.