I LOVE any word that starts with "sn"...snarky, snail, sneaky, snake, snack, etc. I also love "smarmy."
Plethora was an old high school favorite of mine, but it has gone by the wayside over the last decade or so. No worries, though, as I still pull it out of the repertoire every now and again.
I hate to admit it, but my absolute favorite words of the last few years are "BALLS!" and "SHENANIGANS!" (both said exactly as written)