The American Radio Relay League (ARRL)
Largest ham radio organization in the US. Sells many books on a wide
variety of topics. Also has basic information and references.
Top Contesting Web Site on the Net
Twin City Amateur Radio Club Contesters (K9CU)
Champaign-Urbana Amateur Radio Contesting Club (K9CU)
Introduction to HF Radio Propagation
A FAQ on HF Propagation