"By 2004, Webshots was grossing $15M/year, had more than 200,000 paid subscribers, and was the #1 photo sharing site and top 50 media property per ComScore. In the same year, Alexa ranked Webshots the second largest English language privately held Web media property (behind weather.com)."

I won't count Twitpics as it was a posting service, not a storage service, but I expect there are a few closures I've missed....