Electronica (though they all have a hip-hop flava too):
Autechre - Radio mix (promo mix they did mostly featuring remixes of theirs for the release of Chiastic Slide)
Buddy Peace & Zilla - Watch and Repeat Play (Bonus mix that came with the Warp Vision DVD mashing up literally loads of Warp classics)
Quite like Coldcut's Essential Mix as it's like an extended Journey By DJs, but a lot of people feel let down by it just so you're aware
Scratch Pervert's Essential Mix, Badmeaningood Vol.4 and Fabric Live 22 all great in a similar vibe
Spitkingdom Presents Beni B (Mixologists) - (Killa Kela's Spitkingdom mixtape, great cut-up of popular tunes. Can't find any links, have CD if peeps wanna borrow)
DJ Skully - Champion Sounds (DMC mix series with a UK Hip Hop flava, the Plus One and Mixologists ones are worth checking too)
DJ Spinbad - Fabric Live 14 is criminally underated for old skool vibes too
Along with The Scratch Perverts - Fabric Live 22, DJ Yoda - Fabric Live 39, Annie Mac Presents 2010, and the Dirtchamber Sessions Vol.1 all deserve props for being harmless good fun that save many a situation involving a broad mix of people who would otherwise all be taking over iPod dock DJ duties. (Plus obligitory nod to 2 Many DJs - As Heard On Radio Soulwax Vol.2 on that note)
Chemical Brothers - Live at the Social Vol.1
Drum & Bass:
Have a soft spot for Andy C's original Nightlife series, particularly 1 & 2 were great at the time, but like a lot of mixes have aged quite a bit
... Hmmm, I got a bit carried away there, apologies...
In all fairness though I could've carried this list on for ages with the number of mixes that have come, been on constant rotation, and gone, but I'd say the ones above particularly impressed me at the time and I still go back to occasionally. The Nicolas Jaar ones will be there in time, but I don't need to plug them on here!