Bit like trying to pick the best rock album.
Anyway, here's a few must have hip-hop albums.
PE- Fear of a Black Planet
Dangerdoom- Mouse and the Mask (You're a fool if you don't own this album)
Def vs Doom w DJ Phonetic- Mix Bag
Roots Manuva- Awfully Deep/Alternately Deep & Run Come Save Me
Cypress Hil- Black SUnday
Deltron- 3030
Busta Ryhmes- The Coming
A Tribe Called Quest- Beats, Rymes and Life
De La Soul- 3 Feet High and Rising
Wu Tang Clan- Wu Tang Forever
Ol' Dirty Bastard- Return to the 36 Chambers: The Dirty Version, and Nigga Please
Jay Z- The Blueprint (god I wanted to hate the guy, but fuck its a top album. Also dig the by-line to this album release. An album that was tightly kept under wraps throughout production, then announced a week prior to release, Sept. 11th 2001. Long story short, album released, planes crash, WTC collapses, America left reeling, only 16 000 albums sold in first 4 days of release, 3 days out from chart debut and The Blueprint was shaping up as hip-hop's biggest commercial flop, in last 72hrs it sells in excess of 430 000 copies to debut not only at number 1, but also as hip-hop's highest selling debut album.)
Bliss n Eso- Flying Colours
Urthboy- Distant Sense of Random Menace