The most successful companies to come out of Y Combinator

1 - Airbnb - $31bn valuation
2 - Stripe - $20bn
3 - Cruise - $14bn
4 - Dropbox - >$10bn
5 - Instacart - $7.6bn
Source:  Techcrunch, 17th Oct 2018
(Link has top 20, with current valuations)