Back in 2010, everything was about mashups. They were probably more prevalent than remixes, as everybody and their mother figured out how to overlap two tracks on their laptop.
The truth is that mashups have a tendency to suck (much moreso than remixes). So, this list doesn't contain 10 tracks, but rather represents a "best of" lineup for the song mix category. It might have been longer, but I didn't want to over-represent folks like The Hood Internet and Carlos Serrano.
Oh, and just for shits and giggles, I threw in Bastille's silly mashup of The xx vs. TLC at the end.