Funcken - Premier Empire
A good number of plates on the French. Use the "Prec" and "Suiv" links up in the top left to browse through different pages under the same heading.
Leinhart and Humbert - Les Uniformes de l'Armee Francais
Combines brevity (uniforms are condensed into a square) with detail. Scroll down to the bottom of the page for a key, in French.
A huge list, ordered incomprehensibly, and in German. Fortunately my German extends as far as basic country names, which is about all you need for this.
The link goes to French Line Infantry, but the links in the top right will take you to different pages, most of which have a big link to Uniforms. Follow those and look for links saying Planches de Knötel.
This site used to have terrible terrible navigation. They've redesigned it to have better navigation, but now they just dump a bunch of plates on you making you open each one to see what treasures it might contain.
A much better side, but only covering uniforms for the 100 days campaign. Pick an army, then a branch of service, then a regiment and finally click "Uniformes" next to the flag to see the plates.