Is there a usable Namecoin GUI client? Is there any GUI client that is capable of trading Namecoin, and is somewhat trusted by the community?
Multicoin can be used to trade Namecoin although the functions for registering names and such cannot be used.

There is a current bounty of 750NMC to produce a web UI for the client to run within a local machine. It can be found on the http://dot-bit.org wiki site.