If you’re bored of Lorem ipsum doler for your mockup text, this Dummy Text Generator is brilliant. It gives you a range of prose styles to choose from.
(Of course, 37signals “Just say no to Lorem Ipsum", but that’s for another debate!)
A List Apart has some good articles in the usability, UI, design arena.
GUUUI is a good resource for interaction design.
Designing Interfaces: Patterns for Effective Interaction Design. Some good thoughts here about UI designs. The full book is online. Some of it is a little old-school, but otherwise incredibly useful.
Great colour picker from Adobe: Kuler
