I just made a friend a Grateful Dead flash drive "starter pack." Some easy entry points and 'key' years, but not too much at once so he won't feel overwhelmed. It includes:

- 2-11-69 Fillmore (two-disc)
- Europe '72 Vol. 2 (opted for this instead of the original album because there are more jams; specifically the DS>drums>O1 from 5/7.)
- One From The Vault (8-13-75 - this is the one that got me hardcore into the band.)
- 5-8-77 Cornell
- Go To Nassau (May 15/16, 1980, a horribly underrated entry-level live album!)
- Wake Up To Find Out (3/29/90 w/ Branford.)

I also included a (mostly) studio compilation, covering all the albums from '67-'89.

The Golden Road
St. Stephen
Turn On Your Lovelight (Edited Skeletons version)
Uncle John's Band
Casey Jones
Friend Of The Devil
Sugar Magnolia
Box Of Rain
Truckin'
Ripple
Bertha
Not Fade Away> Goin' Down The Road Feeling Bad
The Wheel (Garcia)
Cassidy (Ace)
One More Saturday Night (Ace)
Looks Like Rain (Ace)
Playing In The Band (Ace)
China Cat Sunflower> I Know You Rider
Mr. Charlie
Eyes Of The World
Stella Blue
Scarlet Begonias
Unbroken Chain
Help On The Way> Slipknot
Franklin's Tower
Terrapin Station
Shakedown Street
Good Lovin'
Fire On The Mountain
Alabama Getaway
Feel Like A Stranger
Touch Of Grey
Throwing Stones
Foolish Heart
Standing On The Moon

I'd say you can't go wrong with any of these if you don't already have them.