Ok, I'll comment on as many of these as I can.
Arctic Trooper - Very nice, I think all you need to do is add some sort of Republic/Imperial isnignia to a shoulder.
Stormtrooper w/ trenchcoat - That's a smooth looking custom. Are the arms still articulated?
Trenchcoat w/ AT-ST helmet - Very nice, I love how you smoothed the buttons off the chest. Wish I was confident enough to do that too.
Piett - Looks good. Did you use a Motti body?
Corps head droids - Wonderful, especially the first one. They really fit in well with the Star Wars look.
Gamor - Looks like he came from the cartoon series! Maybe dry brush him a little for some added realism.
Trandoshan - Easily the best in the bunch I think. Wow! What legs did you use?
Imperial Whipper - I like it a lot. Whip those Wookiees! Also, if it could be pulled off, a more "electrical" looking whip would look great.
Clones - They all look nice, especially the gray one w/ removable helmet
Twi-lek - Now that's what I like to see! Good color choice.