NX allows you to remotely access a Linux or Solaris machine and makes applications using X Windows appear quite responsive even over slow links. It even supports resuming, from anywhere, a session with the server suspended for any reason (for example, a broken network connection). The "Free Edition" of NX is free for personal use. The core NX libraries are Free Software. There is also FreeNX that provides a Free implementation of the NX server licenced under the GPL.
NX performs incredibly well, especially when you compare it to VNC, ssh with compression and X forwarding, etc. The desktop client, especially on Windows, still has a few bugs that are mildly irritating but nothing catastrophic. The sheer improvement in the response of your remote applications more than makes up for these minor shortcomings.