For better or worse, these are the things that have impacted my life the most over the past ten years:
Movie: Batman Begins
This was the ultimate payoff for me, growing up with the animated series and the comics. It did everything a Batman movie should and then did a whole lot more, trumping every single other superhero movie that came before it (and a bunch of them that came after). Yes, its sequel took over the universe and is undoubtedly a fuller, richer experience in filmmaking, but from a purely 'Batman' perspective, this one will always be more special and more enjoyable to me and seeing it with my friends, the day after my exams had finished, was the absolute highlight of the decade.
TV Show: Smallville
Ugh. Yeah, it got really bad, but it started when I was eleven and I followed it through more or less the entirety of the decade. It is kind of outrageous that it's been on so long, but I can't pretend like any other show has had as much of an impact on me, throughout the 00s.
Song: Common People by William Shatner
The only reason I don't cite the Pulp version as well (which is equally important to me) is because it's not from this decade (although I did only properly discover it in the last ten years). Along with a number of other Shatner-related projects, this one always just leaves me scratching my head in blissful cluelessness. The fact that something this absurd can exist is proof that just about anything is possible. Probably the most uplifting song ever, for me.
Gadget: Broadband Internet
The Internet constantly being fast and constantly being active made it a lot more accessible for me. If the Internet had continued in its dial-up form, it certainly wouldn't have impacted me as much as it did.