So maybe I'm a bit late to the party with respect to mashups, but "Like I Absolutely Love You", the mashup of Scritti Politti's "Absolute" and Justin Timberlake's "Like I Love You", is simultaneously disarming and perfect. You can hear it as the first part of Absolutely Daft Girls, found at the Go Home Productions site.
By the way, apologies for those of you who may have come here looking for the *NSYNC fan fiction piece also entitled "Like I Absolutely Love You", described succinctly (I love the photo at the top of this page, BTW) as
a nice chris/justin getting together piece that uses the other guys very well and the moms even better. both the guys are dicks and they're very real about everything. plus, there's this phone message about a dead bird that's wonderful on so very many levels.
In my opinion, this is actually fairly accomplished fan fiction, though I don't really consider myself an experienced judge of fan fiction in general. Here's a sample passage:
"Chris," says Justin. He says it over and over, like a mantra, like reinforced positive thinking, over and over until Chris' name is just another sound filling the spaces between them, until Chris kisses him and Justin remembers how it feels to be a part of something bigger.
Not bad writing, really.