The simple question to start with is "What is a mashup?"
The simple answer is that it is an acapella from one song (the vocal track) mixed with the instrumental track from another song. Of course it gets complicated quickly from there. A lot of mashups take components from a lot of different places and weaves them into something new and interesting.
My first exposure to mashups came from an article in a music magazine years ago, back in the early 2000s, when I read about a producer known as the Freelance Hellraiser spliced the vocal track from Christina Aguilera's "Genie in a Bottle" with the instrumental track from "Hard To Explain" by The Strokes. It was, at the time, mind blowing. The song itself came out in 2001, but it was a year or two before I would hear it myself.
In a world with DJs Earworm and Schmolli, this almost seems quaint now, but at the time it changed my perspective on music. Ask some of my friends, they'll tell you what a pain in the ass that I was about them.
This wasn't really the first mashup. This was just the first that a lot of people heard. People like the Evolution Control Committee were doing mindblowing audio collages that sometimes had social commentary worked into the remix. Their "Rocked By Rape" mix took soundbites from then CBS Evening News anchor Dan Rather to show the exploitative and sensationalistic nature of the evening news.
For me, mashups were the music of science fiction, and the remixers were creating cyberpunk audioscapes for our world of tomorrow. Plus they had a good beat and you could dance to them.
That was then. What about now? The rest of this post is going to feature links to some places around the internet where you can find what I think are some of the best mashups around. They aren't in any particular order and I am sure that I am going to leave something out, so I will probably re-edit this periodically. If you think I should add something to this post, please leave a comment with a link to a site.
One of the things that I love most about mashups is that the community is international, and you get to see some cultural perspectives that you might not normally get to see and you can re-hear music that was once familiar from those new perspectives.
For me, the best starting point is the Bootie Blog. Bootie started as an event at the DNA Lounge in San Francisco, and has since spread around the world. I actually DJed in the Second Life Bootie club a few years ago, and had my music and our dancing avatars streamed into the real life club. Yeah, it was before anyone really showed up, but we didn't care. Those of you in Seattle, be sure to check out the Bootie event there. Their site does a (sort of) monthly list of some of the best mashups out, and they compile a yearly "Best of" as well. You can also find holiday music and an archive of the Dean Grey American Edit mashup album floating around the site as well.
Mash-Up Your Bootz comes from Berlin.
Check out their "Best of" for 2014:
The Bootie Blog and Mash-Up Your Bootz are probably two of the best places to keep current on who is doing what in the mashup scene. They are both also very good for finding links to the producers who are doing these things. Once you head down this rabbit hole, you may not come back.
Another favorite of mine, a collaboration from a few years ago, is the Mashed In Plastic project. Why do I like Mashed In Plastic? Each song on the compilation used music and samples from David Lynch movies (or television shows in the case of Twin Peaks). I love the freakish creativity of this project.
Party Ben is a DJ and remixer based out of San Francisco. His music is very danceable and very fun. His mixes sound simple but they have a complexity to them that is lurking just below the surface.
The DJs From Mars are DJs from Italy who create some really creative multi-source mashups (meaning that they tend to do more than a simple acapella from one song plus an instrumental from another song types of mixes).
Loo & Placido are a remix team from France. Their mashups are a bit trippy, and they seem to enjoy the more chaotic elements of this style of music.
The Hood Internet bases most of their work on hip hop music, mixing them with a lot of indie and alternative stuff to come up with weird new sounds.
One of the best multi-source mashers would be DJ Lobsterdust (outside of DJ Earworm, but there's a link to him at the top of this post). Act quickly (at the time of this post) and you can get a massive .zip of his work from 2004 to 2014.
Last, but not least, is Alan Black. I like him because his work is weird. It isn't going to be for everyone, but SF fans may like his work themed around Inception and Star Wars.
There is enough music linked in this post to give you hours and hours of listening. Check them out and enjoy.