Exsanguination, pneumonoultramicroscopicsilicovolcanoconiosis, and cuddly. I try to use them on a daily basis.

I also like words that mean the exact opposite in other languages. Like "Gift." In English, a gift is usually a good thing... but it also happens to be German word for poison =D
Also, horrorshow. Anybody who has seen or read A Clockwork Orange should know what I'm talking about. Horrorshow comes from the Russian word khorosho, which means good. Horror show, on the other hand, is a combination of English words which means, obviously, a show of horror. Horrorshow = good, horror show = bad.