Most profitable way to spend 5-15 minutes?

I generally have a very scheduled day, as a web developer I often have mini deliverables to clients throughout the day where I must send partially finished work to clients to get feedback before continuing, in addition to scheduled phone calls.

With all of this I find that I often have small 5-15 minute intervals between my schedule that I am wondering what the most *profitable* way to spend. I am sure a lot of warriors also are in this situation from time to time.

At the moment I generally use this kind of short breaks to:
- check out warriorforum.com
- review my business reading list at Google reader and perhaps even make dofollow comments on relevant blogs
- make a quick post to one of my own blogs

I'm just wondering what you guys do? I'd love to make a few bucks everytime I have this kind of spare time.

Like I say in the title, the question is how to make it 'profitable'. I want to make every minute pay!

I know everybody does different things, has different businesses, etc. I am just after the top level ideas.