I hate the Go Compare ad, the Misses loves it!!
Surprised no one's mentioned the ones that use pseudo folk music (for butter iirc).
The Michael Winner ads for motor insurance make me smile for some inexplicable reason, but it is ironic that in reality, the company wouldn't cover him, or any other 'entertainers' (in fact most motor insurers back off if you mention to them that you play in a band!!).