Aside from new furniture or equipment, what can you do to improve the ergonomics of your work environment?

There are several things you can do to reduce the odds of getting or worsening a repetitive stress injury.

One suggestion is to keep hands off the mouse & keyboard as much as possible (when reading, downloading files, etc.)
Taking mini-breaks of up to a minute every 15-30 minutes, combined with gentle massage and/or stretching may prove beneficial.
Mixing task types frequently is another strategy.
Spreading out intensive end-of-year and end-of-cycle tasks is especially important for injured individuals.