The first game I come to think of when talking about zany sound effects is Llamatron by Jeff Minter! Loved that one, much thanks to the brilliant sound effects.
But of course, it really is a great Robotron clone as well ...
yep, there are few games that come close to llamtron when it comes down to replicating the sound of a really busy games arcade
I play llamtron regularly, as it's -still- an excellent game
oh yeah oh yeah oh yeah oooooooooh yeaaaaaaaah
an honorary mention has to go to Robotz for the 'eep' noise that plays when you die, brilliant stuff