At the Front Militaria Excellent source for German and American Repro (sometimes original small items) Militaria.
WWII Impressions, Quality Replica WWII U.S. Military Uniforms Everything is high quality repro (and therefore a bit more pricey) and they make all US items.
Hessen Antique, Your source for Authentic Reproduction German Uniforms, Headgear and Equipment
If WWII Impressions is the ultimate US repro place, this would be THE place for German repro gear. I hear their wool uniforms are the best bang for your buck. (I'm buying my M40 blouse from them and getting insignia from ATF since HA doesn't carry GD shoulder tabs)
WHAT PRICE GLORY WPG deals in US and British.
SCHOESSLER'S SUPPLY ROOM™ - Blank Firing Machine Guns SS-room specializes in semi-auto real SMGs and Full Auto Blank Only SMGs. But if you want jacks or low boots this is the place to go. Theirs are well constructed and you won't shoot hobnails the first time you wear them.
The Most Authentic German World War I I Original & Reproduction Items! Never heard much about these guys, I should ask and see if our German units use them, they have some interesting items for cheaper you don't find in other places.
Welcome to Grigsby Militaria Good place to get a lot of German items (and some US) but you need to contact him he doesn't update his site often so you should email him to find out if he has it in stock.
And of course if you are looking for originals e-bay can be a good place to go if you know what you are looking for and can tell fakes from real. But usually if someone does a good job of proving that something is original... good luck getting it because its usually sitting at 10+ bids. Smaller original items unless they are rare can usually be found and bought easily.