If you do interface design work in Illustrator, check out this User Interface Design Framework, including 290 free vector icons. [Via]
As I’ve mentioned previously, pixel rendering in Illustrator CS5 is much, much improved, so I highly recommend it to Web & screen designers (and not as an Adobe employee, but rather as someone who sweated over such details & who regularly cursed Illustrator’s old behavior).
Previously:
Im curious, what software do you guys use for designing your own interfaces?