I recall seeing this asked before a few times
http://bitcoin.stackexchange.com/questions/2324/what-is-the-longest-time-gap-between-blocks-in-the-last-year--Taken from a google search/reddit Post--
Block 27: 2009-01-10 06:56:13
Block 28: 2009-01-10 15:30:57
Block 168: 2009-01-11 23:39:41
Block 169: 2009-01-12 03:22:03
Block 74637: 2010-08-15 17:02:43
Block 74638: 2010-08-15 23:53:59