Well, I briefly tried to do a cool looking side-by-side picture thing, but my cropping and editing skillz (or lack thereof) on Paint eventually got the best of me and I gave up. The pics I have also didn't really seem to lend themselves to cropping and side-by-side analysis, so I figured I'd just post them in order and you can scroll through them instead.
I'm actually disappointed that I don't have any really good (aka bad) pics from Halloween 2008 when I was around my heaviest/starting weight. I would have saved those pictures on my old laptop which I don't want to dig up, so I was left with the pics I had posted to my old-school Webshots account. Naturally, I was pretty judicious with which pictures I posted since I was not particularly happy with my weight at the time and I was unflatteringly stuffed into my flapper costume. The pics I have are mostly group shots where I've carefully wedged myself between other people, hiding my full size. Nevertheless, here I am in all my costumed glory for Halloweens 2008 through 2011.
Halloween 2008: Flapper... a hair shy of 100 pounds heavier than my current weight (yes, I know I'm sketchy about sharing actual weights!)
Halloween 2009: Devil... down about 42 lbs from heaviest (+58 from current)
Halloween 2010: Pilot/"Mile High Captain"... down 65 lbs (+35 from current)
Halloween 2011: Bumble Bee... down 100 lbs (current)
So there you have it. I wish I had better pics from '08 and '09 but I think the changes are fairly noticeable in my face even if you can't totally see the body. I'd like to do another before/during pic in 10 more pounds, whenever I get there!