Current music is pretty good (if you avoid the pop and country pop crap) - White Stripes, Pete Yorn (looking forward to more from him...believe he does have a new one out), Eminem (ayup...gotta give it to him)
Some great stuff came out of the 90s (Alternative really took the forefront - the whole Seattle sound plus R.E.M., U2 and Depeche Mode still going strong, The Smiths, Liz Phair, Beck, Lucinda Williams on the folk/aternative folk/Americana side)
The 80s sucked, musically, with exceptions (like U2, INXS, Depeche Mode, Violent Femmes, The Ramones - but some of their best stuff was in 79...right at that transition away from Disco - thank gawd!).
70s were pretty lame (that's about what you hear on AOR stations...blech).
60s were rather ground breaking in that rock-n-roll evolved rather quickly from a more pop sound into Led Zeppelin, Jimi Hendrix, etc.) and Jazz made great waves with John Coltrane, Miles Davis, and Dave Brubeck (although, the latter two's greatest works were right on the 50s/60s transition)
50s were definitely ground breaking with the introduction of rock-n-roll (Elvis, Chuck Berry, etc.)
40s were big band and swing-jazz and the start of B.B. King and Percy Mayfield so Blues was picking up, too. And, can't forget ol' Hank Williams
30s...mmm...Robert Johnson...
Before that we had Ragtime and predating that I guess it was classical and some regional folk music.