Grateful Dead albums?

I can't pick just three but if you only have those, you might want a live one. I would suggest something like Europe '72 which has a good mix of short and long songs on it. I'd also suggest Grateful Dead from '71(with Bertha, Mama Tried, Big Railroad Blues and so on). Reckoning is an acoustic live album from 1980 and is really cool if you like more acoustic based stuff. LiveDead is a good far out live album. Nowadays, there's also tons of archive stuff that's been released which is far too much to list here. Don't forget that there are also download sites where you can download unreleased stuff.