Unless you have a particular type of puzzle that you like, your best be would be to check out the highest rated problems. They'll give you a good idea about the kind of thing that we like and you're likely to find on perplexus.
If you do have a specific type of problem that you like (e.g. logic, math, word problems, etc.) all the problems on this site are divided into these sort of categories that you can get to from the home page.
Enjoy!