I felt it would be cool to start a thread on the topic of 40K costumes. I tried posting some replies in the news thread, but it got all screwy on me and I couldnt register for some reason...Besides, sharing info in the forum is so much easier and convenient, not to mention easier to follow!
As a very serious costume maker myself (for the record, i HATE the term "cos-play", that makes you sound like a creepy nerd larper...or worse, a "furry"), I gotta say im extremely impressed with the priest and sister of battle costumes. Very professional. Casting or vacuumforming your own set of armor is incredibly difficult, and they really pulled it off.
As for the space marines....eh. I agree with the earlier comment that the noise marine and dark angel look very....cartoony. The black templars look good...from the waist up. The legs on those guys just look far too out of proportion. Its true, if your going for a space marine costume, you've gotta be at least 6'7", 275lbs and it helps if thats all muscle. ;-)
As for my own costumes, you can check them out here:
http://s193.photobucket.com/albums/z77/mountaincycle661/halloween/
Last year i was a 10' tall treeman, and the year before that was Nightbringer (although everyone just assumed i was the grim reaper...whatever, close enough.)
Pictures of a costume at night, when using flash, really can take away the beauty of a finished costume. The photos dont really do it justice, as you have to see it during nighttime on the street....so much cooler.