Well, in terms of rock, I'll always identify the 90's with "grunge," but that's my biggest area of interest, so I'm a little biased.

In terms of popular music, there's a fairly good theory that we identify each decade with the music that was most prevalent at the end of it. Thus, the 80's was hair bands and Madonna. I think it's hard to say what we most see in the 90's. At least it is for me. Rap and teen pop were the biggest things, and I think rap is the larger of the two. I'd guess that in the future, we'll identify the 90's as the decade of rap.

I'm sure hoping something happens with rock. I still enjoy many bands still out there. Queens of the Stone Age/Mark Lanegan, The Hives/Vines/Strokes, Beck (sort of rock), and Audioslave. Then I'm sure there's a bunch of smaller groups I'm forgetting. If we're not getting a big, new movement, we at least still have some groups still doing their thing, some really well.

Eventually, I think rock will have to share a similar fate with jazz. There haven't been any big jazz movements in several decades, and if they have, they've been more cross-genre. At least that's how I see it.