I paid Spike and Drusilla, from Buffy, to say/sing happy birthday to my wife. Neither are top-tier actors, but they're both completely recognizable James Marsters in particular I guess, as he's done a lot of narration for things like the Dresden Files.

There were "super-popular" actors available, for significant sums, but these two were cheap enough that it was a no-brainer to gamble on a good result, and both were fantastic.