InWorldz has it's own marketplace now ran by the people at InBiz. Works a bit different than the one in SL in that you have to put funds into a InBiz account that's easy to set up. Guess it's more like the old SL xstreet when the two accounts were separate.
I have a few items on there as a test, so far it's working well, deliveries are made across grid quickly:
Random Rosie on InBiz Mall
You can read the FAQ here: InBiz FAQ