As a front-end developer, I'm often given graphics of web sites and told pretty much, "Make it work." I've recently started working on Linux 100% of the time and was wondering if there's any programs out there that're good for "digesting" graphics.

All I do, pretty much, is draw little selection boxes and takes notes on their dimensions; I also slice out a piece of the graphic (i.e. copy out just the part of the graphic I need for to make the same effect in CSS). Before now I've been very happy with Fireworks, but I need something for Linux, any suggestions?

As a note, I mainly deal with pixel based graphics, so the program being vector based isn't a necessity.