If you're looking for the sounds that the SID produces;
odosynths ==> 38911Bytes (donation ware)
It sounds really good, I've been using Odo synths quite a bit now.
If you're looking for adding some dirtiness to your productions and samples...
Akai S-950!
I don't know where you live, but in the Netherlands the 950's are getting really cheap (a good working model, near mint condition..... around 250$)