I can help you with a few books, but I can't think of any good websites that deal with uniforms. Osprey publishes their
Men-At-Arms series. Number 316,
The German Army 1939-45 (2) North Africa & Balkans ISBN: 1-85532-640-X , is a good place to start. It contains 8 pages of color drawings with 3 different uniforms depicted per page. It also includes unit insignias, badges, awards and rank insignias. Another good book is
AFRIKAKORPS published by Histoire & Collections of Paris, ISBN: 2-908182-50-5. This 142 page volume in filled with hundreds of full color photographs of actual uniforms worn by re-enactors. This book is all you will ever need on DAK uniforms. It covers all types of uniforms, personal equipment, insignia, headgear, etc. I paid about $45 for it and it is well worth the price.