Rap,
I don't agree about "bottomless hole" being an oxymoron.
Although holes dug in the earth will normally have a bottom, other holes may go straight through to the other side of something. That makes it tautology rather than an oxymoron.

But, to add to the list:
Rap music (not aimed at the aforementioned poster)
Yes, I know that 'rap' usually has a backing track, but it tends to be the words, spoken in a monotone, which are being described by the term.

Original, improved (seen on a bottle of Nescafe coffee)