Given that my vocabulary isn't as big as I'd like it to be, I signed up for Dictionary.com's Word of the Day some time ago. I save the words I think I'll actually use, and I've recently gotten into the habit of sticking one on an electronic post-it note on my computer so I'll actually see it and learn it.
One of my all-time favorite words has been willowwacks, which Microsoft Word doesn't recognize... but I slipped it into TDSF anyway. It just sounds cool. I also recommend bumptious, incommodious, dandle, and just plain signing up for Dictionary.com's Word of the Day (it's on the left). Today's word is "fey."*
*A word which, if I see on a back cover, will immediately cause me to put a book back on the shelf. That, and "elf."