The canonical place to find hosting recommendations is http://www.webhostingtalk.com .

If you're looking for information about where YC-funded startups are hosted, here's the latest numbers from wikipedia's list of non-acquired, non-defunct YC companies:

   4     SoftLayer Technologies Inc.
   3     Layered Technologies, Inc.
   3     ThePlanet.com Internet Services, Inc.
   2     NoZone, Inc.
   2     Rackspace.com, Ltd.
   1     Amazon.com, Inc.
   1     BitPusher, LLC
   1     Carnegie Mellon University
   1     Columbus Network Access Point, Inc.
   1     Global Netoptex, Inc
   1     ServePath, LLC
   1     Simpli Hosting, Inc