What, in your opinion, is the most Iconic/Generation defining rock song for the years 2000-2010?
I would recommend:
The Killers
All These Things I’ve Done
https://www.youtube.com/watch?v=sZTpLvsYYHw
or
The Heavy
How You Like Me Now
https://www.youtube.com/watch?v=sVzvRsl4rEM
I choose The Killers by a very thin margin
“Seven Nation Army” by the White Stripes
I second this, and also throw in Franz Ferdinand’s “Take Me Out” as an honorable mention.
good choice!
While those EA Sports FIFA anthems are good choices, I’d like to go a bit off the beaten path and nominate:
Wake Me Up When September Ends, Green Day
The Killers. Mr Brightside.
You could not get away from it from about 2003-2010.
Agree with most of the rest and would also suggest
“Sex On Fire” or “Use Somebody” by the Kings Of Leon.
(Unfortunately.)
Sheesh. No need to go there. That wasn’t even the ‘most iconic/generation defining rock song 2000-2010’ named “Someday”!
I’m also going with The Killers, but Somebody Told Me is my jam.
That or Panic! At The Disco with I Write Sins Not Tragedies
Winners right here.
My awareness of popular music during the period in question has been very sporadic. Almost all of the songs mentioned in this thread, I have no idea what they sound like (though it’s possible that I might recognize one or two if I listened to a sample). But these two are indelibly stuck in my head:
So, if “iconic” or “generation defining” implies a song that just about everybody knows, these are the strongest candidates so far. “Hey Ya” in particular was impossible to escape during its heyday. The main objection to them is that they’re arguably not rock songs (but rather, pop).
The most ubiquitous unambiguously rock song I can think of off the top of my head is U2’s “Vertigo” (thanks partly to its use in those iPod commercials). But then, U2 as a band isn’t especially identified with that particular decade/generation.
Strictly rock: My 1-3 would be the previously-mentioned “Seven Nation Army,” “Take Me Out,” and “All These Things That I’ve Done.” If you’re looking for 2010s influence, you could maybe go with Mumford and Sons’ “Little Lion Man” or, more dubiously, Arcade Fire’s “Wake Up.”
Including pop: “Hey Ya!” by a lot, then maybe something from Justin Timberlake – “Cry Me a River” has the Britney dis and the Pitchfork cred, but “Rock Your Body” has the drug/sex references and the wardrobe malfunction. I’ll pick the latter, but just barely. 
Although “Seven Nation Army” is a strong answer, I feel that “Float On” by Modest Mouse gets at least an honorable mention.
Other songs to think about:
“Radioactive” by Imagine Dragons, which I believe is the song from the 2010s that has received the most airplay so far.
“Second Chance” by Shinedown is a typical example of a whole bunch of songs from the late aughts that have a similar sound and/or feel. This would also include songs like “Paralyzer” by Finger Eleven and "How To Save A Life" by The Fray.
Pop punk was also big during this time. Besides Green Day (for whom “Boulevard of Broken Dreams” is probably a stronger candidate than “Wake Me Up When September Ends”), there’s “Fat Lip” by Sum 41 and "Lifestyles Of The Rich And Famous"by Good Charlotte.
One last song to consider is “Sugar, We’re Goin’ Down” by Fall Out Boy.
Yes.
And yes.
Perhaps because I dislike it so much, “Bodies” by Drowning Pool seemed ever present to me throughout the entire decade. Just about every 20 year old in Iraq considered this their theme song in 2003 when I was there. I’ve seen many tattoos based on this song. I don’t want this to be “the song of the decade”, but I’m afraid it probably is.