Reflowster may not work perfectly with every toaster oven, but we've found that smaller, cheaper ovens typically work great because they allow for faster changes in temperature. Most simple toaster ovens without digital controls will work. In particular, a toaster that can be stuck in the "on" position is required. This state needs to persist through a power cycle. Most toasters do this by turning the timer knob backwards.
Remember that you'll probably want to buy a toaster oven specifically for using for reflow soldering. Once you've baked solder paste in a toaster oven, we highly recommend not using it for food. We plan on including Reflowster stickers that say something to this extent to place on your toaster ovens.
If you're in the market for a new toaster for reflow soldering, our suggestion is to get the cheapest one you can find. The cheapest one we found is the Proctor Silex 31111 on Amazon. You may be able to find a cheaper one, but this is the one that we will be shipping with the special edition Reflowsters. It has worked well for us so far and is known to be compatible with Reflowster.