Beastie Boys - Intergalactic is an awesome, catchy track from my youth.
Not surprisingly, there's some really good mashup made using the Beastie Boys vocals that are worth listening to:
Daft Punk + Beastie Boys - Intergalactic Planet Get Lucky
There's actually two Ghostbusters / Intergalactic mashups I've found. The Jamal Bootleg mix is far punchier, but the looped beats are a bit jarring.
For pure listening quality, the Josh Brewster Mashup works really well:
John Brewster - Intergalactic Ghostbusters (mashup)
...and something right out of left field:
M83 vs Beastie Boys - Midnight Galactic