A friend from graduate school sent me a link to this mashup by Bill McClintock recently:
This is an example of a mashup that was constructed in a fairly simple manner, but with maximum results. It begins with the introduction to "Shop Around" by Smokey Robinson and the Miracles (1960). When Robinson sings the lyrics, "and then she said," the guitar riff to "Money for Nothing" by Dire Straits (1985) comes in, replacing the Miracles' original accompaniment. This riff underlies all of the verses in "Money for Nothing," and serves the same purpose in the mashup.
Neither track is transposed, as both are in G in their original contexts. Smokey Robinson's voice was originally harmonized by G and C dominant seventh chords; in the mashup, these have been replaced by a G minor seventh chord and a C major triad. Regarding melodic/harmonic fit, the new context works incredibly well. The choruses from "Money for Nothing" feature a different chord progression, but when this happens (at 1:24), Robinson's voice cuts out, and Mark Knopfler sings his own chorus. This means that there has been a section that was only Smokey Robinson and the Miracles, a section that was only Dire Straits, and (the biggest) section, where they were mashed together.
Then, at 2:08, the unmistakeable voice of David Lee Roth comes in, shouting, "Oh, no!" The Dire Straits guitar riff continues, but now it's overlaid with Eddie Van Halen's guitar solo from Van Halen's cover version of "You Really Got Me" (1978), originally by the Kinks. The guitar solo has been transposed down by half step in order for it to fit with the new G minor context.
I'm not sure about the Van Halen, but the other two songs have a clear connection: money and shopping (hence, McClintock's title). The Smokey Robinson song recounts (with lighthearted 1960s sexism) advice given by the singer's mother: to "shop around" for a woman to marry, rather than settling for the first one to come along. "Money for Nothing" was actually a rather controversial song when it was released, due to homophobic lyrics that have since been removed from most versions (including the one used in this mashup). It was written from the point of view of a man working in a department store, trying to sell appliances and televisions. The title references his thoughts about musicians on MTV who get "money for nothing and chicks for free." It's always satisfying when two songs that connect on the level of subject matter also connect melodically and harmonically, as these two do.