[devilsadvocate]

In no particular order,

U2
Avenged Sevenfold
Rolling Stones

I disagree with MJK's choice of the Beatles and the Who. Every kid who ever picked up a guitar and wrote a song to get the attention of a girl owes a debt to Lennon and McCartney (sorry Elvis fans, he didn't write his own hits and was washed-up halfway through his career). Come to think of it, any successful band who wrote their own material owes them; everything else was by professional songwriters (kind of like today, which in itself would explain quite a bit). Why doesn't this apply to the Stones, you may ask? Because the Stones chased trends, and when they were too old to chase trends they went corporate; "Exile on Main Street" really was their last good album. Outliving your contemporaries doesn't make you great.

I wasn't aware that anyone thought the Who were timeless geniuses, but I was windmilling to "Pinball Wizard" and "Won't Get Fooled Again" when I was 3 so they qualify as influential, regardless the pretentiousness of the Rock Opera concept. We won't hear that kind of songwriting ever again...not even from Townshend himself.

I would be interested to hear what would make the Beatles and/or the Who overrated; that must've been a fascinating conversation and I'm worse off for not having been a part of it.

EDIT: Honorable mention goes to Ritchie Blackmore...I always like me some Deep Purple/Rainbow, but the guy's really not all that great a guitarist, and this is coming from a musician.