There have been 23947932985 combinations of "Toxic" with the instrumentals of almost every song it seems, but almost none have been half as pleasing as the original. I will say that there is a "Toxic" ~Rock Version~ that I found that is quite decent and that Linkin Park mashup is pretty nice too.

Having said that, I am usually a fan of mashups, with my favorite two being "Ur+Ur Hand 4ever" and "Justin's Not In Love," both by Cropstar.