At one end Dan Mei bring his "Perfect Sober Insanity", a hardcore mix built on Disturbed's (http://www.disturbed1.com/) "Perfect Insanity". What really makes this work is that he's mixing against Pink's "Sober" (http://www.youtube.com/watch?v=jxexx_TdneA). Most of Pink's stuff is pop, but she's got a strong R&B background and you can find a lot of darkness in her tunes. Dan Mei matches the two hard and darks perfectly.
Speaking of darkness, Depressed Mood... err, Depeche Mode are the original that a thousand emo bands want to be. Here we get Marc Jonce going the opposite direction from Dan Mei. Starting with Depeche Mode's very dark "Suffer Well" he plays off against Empire of the Sun's "We Are The People". Like DM, EotS are electro-pop but with darker undertones. Jonce mixes it up, giving the track a dancier and less metal feel than the Dan Mei.
Moving farther toward dance but with a bit of an edge, we have The White Panda (http://www.last.fm/music/The+White+Panda), another pair of remixing DJs. This is a three-way mash, but I'm not familiar enough with the original artists to tell you which tracks are being sampled.
About a year ago Chromeo released a wholly uninteresting modern disco track "Night by Night" (http://www.youtube.com/watch?v=DmbdtbdBqI0). I've heard the vocal bits from it lifted here and there. This time, DJ U-Tern (http://www.myspace.com/djutern) takes not just the vocals but some of the R+B feel and mixes it with Daft Punk-esque modern electro. The result is a whole lot better than the original.
ElectroSound (http://www.electrosound.eu/electrosound-bootlegs-mashups.php) a European duo have taken a popular RHCP track and paired it with The Golden Filter (http://www.last.fm/music/The+Golden+Filter) to give us a more relaxed and ambient take on RHCP's psychedelic influences.
RCRD LBL presents two remixes of Boris' (http://www.myspace.com/borisdronevil) "Buzz In". Both have a nice ambient feel to them, without being drone-y, the kind of thing you'd wind down a dance set with.
Finally, we have this beautiful ambient piece from Ben Rymer (http://www.rymerindustries.com/). It's synth and swoosh and all that you'd expect from ambient but there's still a beat here.