Free RF Simulation Software

For normal lumped circuits, your favorite version of spice will work fine.

For analyzing matching networks, I've used gsmc.

For analyzing a layout and extracting parasitics and computing fields, I dunno. It's usually easier to just build the circuit and see what happens.

Be sure to check out QucsStudio. I've just started with it, and it seems too good to be true. These guys put more work into their documentation than most freeware has in the code. Very nice!!

http://dd6um.darc.de/QucsStudio/qucsstudio.html

Also, this site has a free Smith Chart, RF Filter, and Opamp filter design programs that may be useful to you.

http://www.iowahills.com

HP AppCAD, available from: http://www.avagotech.com, may be helpful