Haven't been here in, what, years? Anyway, I occasionally run across an artist I think should be mentioned to STYX fans. I mention these two artists because I also happen to like them, not necessarily because they remind me of STYX, although one has an amazing voice (and good lyrics) while the other has amazing lyrics, both of which are important STYX traits.
1) Katie Melua - Especially her Piece By Piece album. Amazing voice, well worth a listen. Extremely versatile, this album ranges for pop to blues to jazz.
2) Leonard Cohnen - What can I say, he's been around over 40 years now (as a musician and songwriter, but even longer as a poet and novelist), and somehow I had never heard of him until recently. Absolutely amazing lyrics. Give a listen to his live version of "Everybody Knows". Also check youtube (or iTunes for a high quality version) for his "Closing Time" video. He may writes some of the most interesting and intelligent lyrics I've ever heard.