I've been excited for this all month, and it is finally here! DJ Earworm's United States of Pop mash-up for 2010:
I never thought I could tolerate Ke$ha in any form, let alone Katy Perry, but this mash-up manages to make them listenable...
You can watch 2009's mashup here, and 2008's here, (that one's still my fave).
Here's DJ Earworm's post about the song, which includes a link to download the MP3.