YC Faq states
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The ones that are currently launched are: Reddit, Loopt, ClickFacts, TextPayMe, Snipshot, Inkling, Flagr, Wufoo, YouOS, LikeBetter, Thinkature, JamGlue, Shoutfit, Scribd, Weebly, Virtualmin, Buxfer, Octopart, Heysan, Justin.TV, I'm In Like With You, SocialMoth, Xobni, Versionate, Adpinion, Anywhere.FM, Fuzzwich, Bountii, Auctomatic, Disqus, Draftmix, Webmynd, RescueTime, Reble, Heroku, Tipjoy, AddHer, and 8AWeek.
-- Some of these don't seem active (e.g YouOS blog was updated sometime in 2006). Is there a list of the active ones? Wikipedia seems dated too ...