I thought about trying to find the best C3PO costume I could find on the web, but instead thought I would post the C3P0 costume I wore for 3 years back in the 1980s. I had originally asked to go as someone from Star Wars (I was thinking Han or Luke), but I somehow wound up with 3PO. I cannot say it was a popular choice and I also cannot tell you why I wore the same costume for multiple years, especially when in the last year it needed to be stapled together. Great mysteries of my life I guess.
Here is a pic of the costume via Star War.com — I cannot find a pic of me in the costume anywhere.