Lester Young

Lester's recorded work falls into two fairly distinct periods: when he was a member of Count Basie's band, and when he was the leader of the Lester Young - Teddy Wilson quartet in the 1930's and into the 1940's; and the post-World War II period when his playing had deteriorated following his experiences in the military. Rather than give you a laundry list of recordings with my subjective evaluation, I suggest you take a look at AMG's music service which rates most of Lester's better recordings. Here is the link to AMG's page on Lester:
http://www.allmusic.com/cg/amg.dll?p=amg&sql=B0ud7yl6jxpsb

The Lester Young Trio with Nat cole and Buddy Rich is fantastic as are the Complete Aladin recordings.

If you are an LP guy I recommend that you try to get him on LP rather than CD. I find those old jazz recordings sound much more alive on LP.
I'm not a huge lester young collector, but I really like the 'Lady Day and Pres 1937-1941'