Wufoo did YC then didn't raise a Series A, before eventually selling to SurveyMonkey. Olark raised from YC, then a Seed and that's it. Statuspage did YC and then Seed and then sold to Atlassian. These are just some examples off the top of my head, I'm sure I could come up with a ton more.
Thanks for these examples. Going for a relatively early sale/acquisition/acquihire returns capital to the seed investors, so not really quite the scenario that I was thinking of, but the Olark example is very interesting.