Probably not the slickest site on the net, but the Tar Water Mess site well makes up for it in navigation, information, and pure heart. This group is also home to many of the movers and shakers in the authentic movement of Civil War reenacting in the US.
The areas to pay the most attention to are the Links and Mess Mates sections. The Links page gives many links to vendors who aren't very visible in other places, but would seem to be great sources of items. I have an automatic appreciation of any site that does a write-up on its membership. You can put a face to the people of this group, gives you an idea to their authenticity level, and it simply makes the hobby look fun. The TWM site does just that - makes it all look fun.
All in all, I like this site and I recommend giving it a visit.