I cant for the life of me find the post I was reading the other day that listed a few other sites similar to theme forest. I will keep looking and update it if I find it.
However, if you check out the other sites by Envato such as FlashDen, you will see there are a few other outlets in their network to sell your work. Flash den is obviously Flash components, but you can write tutorials for the PSDtuts or vectortuts sites and such as well.
I havent yet put anything up for sell, but I see how well they promote their network so it seems like a strong market if you have quality work to sell.