Okay, so since seeing the Calvin and Hobbes costumes at
http://www.craftster.org/forum/index.php?topic=394017.0, I know realize that none of us deserve to win like those two.

But in any case, here's my entry. This is the first time I've been able to actually post a homemade costume for this contest. I actually started it in August and it's the biggest, most involved thing I've ever sewn because I'm not much of a seamstress.
My husband bought Yoda's FX lightsaber for me last year for my birthday so this idea actually took this long to come to reality. Only the lightsaber, boots and D ring belt were bought. The D ring belt was saved from the thrift store bag, once my husband was going to toss it out. The boots I wear on a regular basis.

I actually sewed this costume two separate times, from Simplicity's Jedi knock off pattern, #5840. The first time, it turned out horribly, even with making several tweaks and taking it in a few times. I switched from the cheap Royalty Broadcloth I started with and switched to a better looking and better hanging linen-type fabric. This is light enough to be comfortable outside during a southern Virginia Halloween.
One Jedi costume site recommended using ties on the inside for a more secure, tighter fit. I'm actually using snaps on mine. There are snaps in the shoulders, and the other half of the snaps are in in the tabbards to keep them from slipping down over my shoulders.
I also put in a set of shoulder pads, but I actually put them in backwards on purpose. According to the Padawan's Guide, "Obi-Wan's tunic has a noticeable "tuck" where the sleeve joined with the shoulder. In Ep. II, particularly in the scene where Obi-Wan is floating in those electric cuffs, you can see a shoulder seam too." I am wildly happy with how this turned out. I changed the construction of the collar and added the interfacing.
I tried to follow the pattern for the belt and tabbards but they weren't long enough, so I abandoned the pattern completely for it and just winged it, by looking at lots and lots of photos of Ewan McGregor's costumes instead. The "official" costuming sites, like the Rebel Legion and the Jedi Assembly, were great in explaining the details of the costumes. I didn't try to copy the younger Obi-Wan's costume, which is why I went with slightly different colors for my costume, but I liked how the tabbards were tunic-length in the front and stopped at the belt in the back. That little detail makes it standard as an Old Republic Jedi costume.
The dickey was the first thing I made and the only thing I didn't have to remake. I didn't even have to tweak the pattern. This was a random remnant from my stash that I bought for this costume, I just wasn't sure which part I'd use it for. The pattern called for making your own ties to help secure it around your body, but I had white ribbon so I used that instead.

I realize in looking at this photo, I should have pulled down the back of the tunic a little bit before my husband snapped this one for me.
These pants are actually from a woman's pirate costume pattern:Simplicity 3677 Misses' Pirate Costume Pattern. I thought I had elastic when I was almost finished with them. Turns out I didn't, so I ran down to Walgreens. I was denied there. Their tiny little sewing rack didn't have any elastic and I just didn't feel like going any further. I dug through my stash of stuff and came across a fitted sheet I had used for a different project. I cut a bunch of elastic from it and reused it for these pants.

And yeah, dress a grown up in a Jedi costume and put a lit lightsaber in her hand and it's impossible to not grin, wave it around and fight invisible Sith.