The main thing that attracted me to penturning was having a reason to collect and use a variety of woods. I haven't taken the time to get a complete inventory of the different species that I have now, but I'd say its well over 100. Sometimes I just sit and sort through blanks with no real purpose -- I know, I'm strange. Anyway, I've tried to come up with an answer to this and every time I try to narrow it down I just get lost and give up. But then I thought, "what woods are my least favorite?". For that question I have an answer - I turned a Makore pen once that was so plain and boring I almost didn't want to give it away. Unfortunately the coworker that I gave the pen to really likes it, so I have to see that crappy looking wood about once a week. I'm also not a fan of straight grain oak (yes this includes the whiskey barrel pens) -- I think that I split (by hand) too much white oak for firewood, it brings back painful memories (like actual physical pain). The last one that makes my list of dislikes is Jatoba, I think it looks ok for larger flatwork, but the pen that I made from it looked like a turd - dull, plain, and brown.
I'm not too surprised by the lists of likes generated by others. In addition, I'd put texas ebony, oxhorn bucida (bulletwood), bocote, cork burl, imbuia (smells wonderful), cocobolo (I'm not allergic yet). But man, the more I think, the longer my list gets.