Our team uses Skitch a lot. It’s a pretty invaluable tool for communicating visual information – you can easily annotate screenshots or comps. There’s great communicative value in being able to point at something, and as a remote employee in my past two jobs, I can’t imagine ever collaborating on web work without it.
Skitch does a lot of things well, but one bit of polish which always pops out at new users is the “Click to Clipboard” functionality. Skitch provides lots of ways for you to share your images, and when you click in the appropriate field, the site copies all the data to your computer’s clipboard, and presents a nice confirmation that you’re ready to paste that elsewhere.