Companies which have publicly disclosed that were rejected by YC and have since raised >$20m: * Chartboost * Sendgrid * LightSail I've seen it claimed that Couchbase should be on this list, but I've never seen a primary source which verifies that they were rejected from YC.
http://damienkatz.net/2006/11/how_not_to_pitc.html
Whether that counts for Couchbase is another question.
(I guess it probably does)