Heres what I know:

There are action figures, (aren't there always?), and most are expensive and harder to find than other stuff.

There are interative pets like Tamogachis, however, these came out before the showor anything, making them the original digimon.  I still like the show more...

There are new digivice things that you shake to digivolve your digimon, and then battle against others with the toy.  It's cute, but appears to be one of those five-second-fad kind of things.  I wouldn't advise buying one.

There are cards, and lots of them, but these are actually a big ripoff of Pokemon Cards, or so says me.  The show and toy are unique, but the cards scream "ripoff!  ripoff!  Marketing scam!"  If you like them, I hold nothing against you, becuase I like Pokemon cards, and they were a ripoff of Magic cards, and Magic cards were a ripoff of the Dungeons and Dragons geekathon.  Still, they're probably cool, and by now I'm just typing to fill up space.  If you read this far, I dub you as Sir Patient.