Beardsley
Beardsley’s good, but he was out-Beardsleyed by Harry Clarke, the great Irish stained-glass artist, who did phenomenal illustrations for the tales of Poe and Hans Christian Andersen.
http://web.ukonline.co.uk/archer/poe.html
After Clarke, my favorites are Edward Gorey and Lee Brown Coye. All pretty morbid, but that’s me.
Does Norman Bel Geddes count as an illustrator? If so, I’d like to include him for his evocative futuristic cityscapes.
I second whoever said Norman Rockwell. Also, I recently got a book called Legacy, a collection of artwork by Frank Frazetta, and I am much impressed.
Traditional Illustration: Franklin Booth
Comic Books: Travis Charest
other artists: Doug Webb, Ralph Goings and Paige Columbia Oden
I like Keith Parkinson. Or at least, I used to, but he’s getting a bit uninspiring recently. All his work for Everquest is annoyingly traditionalist.
I studied Illustration at Otis College in L.A. I strayed to pottery, but still love Illustration. I’ve sold a lot of artwork (and pottery) at Science Fiction conventions. Not that I was ever that great at Illustration - portraits are more my thing.
Someone mentioned Dave Stevens. Dave Stevens was in a class with me at Otis. (Nice guy, from what little I remember.) Burne Hogarth (from the old “Tarzan” comics) taught there for a while. GREAT teacher! I took two semesters of his classes on Figure Drawing. Needless to say, there were quite a few illustrators and artists attending the classes, since Hogarth is quite a legend. (His books still sell well.) Dave Mattingly (who does a lot of book covers, used to work for Disney) took a semester. A really nice guy - really humble and down to earth. Hmmm…who else. Paul Chadwick - anyone heard of him? He did a comic book called “Concrete”. OK guy. There were more - I can’t remember them all.
As far as my personal favorite illustrators - I like Hogarth’s work, Paul Chadwick did great with “Concrete”, Dave Mattingly’s Disney work is great. Dave Stevens’ work is really nice too. Other favorites are Tom Hall (book covers), Norman Rockwell, William Reiser (funky stuff), Pat Nagel (I have a Pat Nagel story from Otis - but I have to stop name dropping now!) and…lemme see…the guy who did “Dinotopia” - he did an art demo at a WorldCon once - WHAT a great guy! Oh! His name is James Gurney. What a great guy, and FANTASTIC artist!
I’ll stop now.
I personally love his “nature” paintings - the Shire, Edoras, Minas Tirith, stuff like that. The atmosphere he creates through color and style always seems to fit with my mental image of the books. As far as hobbits go, I agree with Fiver - but I really love some of his elves (ex. Luthien Tinuviel, NOT Galadriel).
I think Alan Lee’s style is much more “fantasized” than John Howe, whom I also really like, incidentally. Howe’s style is much crisper and more realistic than Lee’s.
Ok I’m having difficulty explaining this well 
PS - thanks to lovelee for linking to Tony DiTerlizzi. I love his illustrations in the Planescape books and the Monstrous Manual (2nd ed.).
I really enjoyed Concrete; only have a few issues, but they’re among my favorites from my brief foray into comic buying.
My favorite is N.C. Wyeth. His work illustrating Kidnapped, The Black Arrow, Robin Hood, The Last of the Mohicans and especially Treasure Island just leaves me in awe. Of course it helps that I’ve been able to see some of the orginals of these.
Another favorite is Frank Schoonover.
Yup. It’s currently out of print, for numerous reasons. It didn’t tap the M:TG/Pokemon market, obviously. It was also like marbles–cards you capture, you keep, and this is pretty strictly enforced because once the cards are put in play there’s no mechanism for telling them apart. That makes it harder to build and tweak a deck, but for someone like me who’s not a huge strategy freak, that was kind of nice. You just play for fun–which means that you don’t constantly have to be buying boosters to get the make-or-break rares.
A shame it’s dead, really, since it was a fun game, with innovative but very simple mechanics–and very amusing art, of course.
Ender, I believe he did the covers on Asprin’s MYTH series, at least on the Starblaze (trade pb) editions. Also did internals.
Also like the Frazetta and Vallejo covers for the REH Conan books.