I bought the Comm1 VFR and IFR CD's. They really helped my "radio". I highly recommend them...I will second the recommendation on Bob Gardner's book...
If you buy the Comm1 stuff...spring for the headset....you will be glad you did.
Matt - I stumbled across this AOPA resource and it is very interactive and helpful. Go through the course and I'll guarantee you learn some good tips. Wish I found this when I was training. http://flash.aopa.org/asf/radiocomm/swf/flash.cfm?