For cool of the superlative sort, try Seven Steps, the seventh Miles Davis boxed set from Columbia. The seven-CD package of sessions related to Davis's 1963 album Seven Steps to Heaven features drummer Tony Williams (19 then, and explosive), Williams's near-contemporary Herbie Hancock on piano, and bassist Ron Carter. The anomaly was George Coleman, a tenor saxophonist in the unfortunate position of predating Wayne Shorter, one of Davis's most formidable colleagues.
The box also includes seven tracks never released before, some with interim saxophonist Sam Rivers (who went on to an eccentric, brilliant solo career) and a side with Shorter, the key to Davis's second great quintet (the first, from 1956 to 1961, included John Coltrane).
The tracks with the more obscure Coleman dominate. He comes off as soulful but orthodox, creating a tension that likely spurred Davis -- never one to forgo a challenge -- to the more adventurous Rivers and, finally, the daring Shorter. This box, which also features great live dates from Tokyo, Berlin, and the New York Philharmonic Hall, is an intellectually fascinating documentary of musical growth.