Authors who are great at characterization..

My favorite author is Lois McMaster Bujold.

After her, I find that I prefer (in no distinct order) James Alan Gardner, Dennis Danvers, and Robert J Sawyer.

All of the authors are simply great at characterization, tend to be good at humorous dialogue, and typically they avoid plot problems. Does anyone have recommendations of sf/fan authors with similar writing skills?

For science fiction, I think that Frederik Pohl is usually quite good at characterisation, but that is just one person's opinions. The few books that I have read of Ursula LeGuin have been extremely well-characterised too, but others with more reading experience of her will have more authority on her.

Other authors outside of SF that I like for their characters are David Gemmell, a fantasy author, who creates realistic characters that I love or loathe, simply by giving me that character's entire life story in a page, and John Grisham, who can create a realistic character, with some of their major life events (not as well-fleshed as Gemmell, though) in a paragraph.

However, all of these are just one person's opinions.

I'd probably suggest Karen Traviss and Kage Baker. Karen's works down' have much humor, but I think that both are very good at characterization and plotting.

Steven Brust's Vlad Taltos series (start with Jhereg. Elizabeth Moon especially her Hunting Party Series.
Patricia Wrede both her Lyra series and her Dragons series.
Terry Pratchett's Vimes books in the Discworld series, and also the Tiffany Aching books.
Nina Kiriki Hoffman All of her books. Except Catalyst.
Diane Duane Any of her Door Into... books Door into Shadow is the first.
Robin McKinley
Guy Gavriel Kay
Jane Lindskold Her Changer duo and Child of a Rainless Year
Connie Willis Bellwether, To Say Nothing of the Dog
Diana Wynne Jones

I love Bujold too, and am giving you my other top favorites!

For dry humour:
Death of the necromancer by Martha Wells,
The better part of valor by Tanya Huff,
Lady in Gil by Rebecca Bradley
pagan's crusade by catherine jinks

For good characterisation: c j cherryh, barbara hambly, rosemary kirstein, beth hilgartner, helen s wright, kage baker, kristine smith,
jennifer wingert

I'd strongly second Kristine Smith, and Guy Gavriel Kay, and Wells' Death of the Necromancer and further add R. M. Meluch, Sarah Zettel's SF or fantasy, both are smartly characterized, beautifully plotted, and nicely finished. In fantasy, also try Barbara Hambly, Sherwood Smith's Inda and The Fox, and anything by Carol Berg.

Octavia Butler is great at everything:-)

Yeah? By my count, great Butler noir is non-existent. ;-)