Long and detailed guide to creating Wordpress themes from scratch. Has a Windows bias in places but to be honest I've not worked through it as I have no personal desire to create a theme from scratch. If you're not prepared / able to pay someone this could be the answer.

Theme with javascript sliding menu thing at top

Business-ey Wordpress themes

Some nice ones here.

Clean three column WordPress Theme. Handy for sites where the content is the most important thing. (Um, like all of them?)

Nice looking Wordpress theme with more there too.