I myself just got this off eBay (should arrive tomorrow):

Tapco SQ2 Compressor/Gate
It's supposed to have much better circuitry than the Alesis 3630 and the like, but what makes it interesting is the "AIR" function. Basically a post-compression HF exciter that should be a lot fun to play with.
I'm looking forward to making some super compressed sounds and seeing what kind of character I can get from abusing them with it. Also, I've been running some stuff to cassette recently, maybe I'll put this in the signal chain as well.
Price - £37. And that includes the shipping. And the guy is even throwing in some jack cables to boot. SCORE!
Basically, if I use it even just a few times it will have been worth it.
Who else made a good buy recently?