Every place I've worked for a reasonable time, I've made it a condition of my employment that there be ergonomic accomodations made. Here's what I ask for (and have always got):

• LCD Monitor, 17" 1280x1024 450:1 contrast (or better); reduces eye strain (for me: it's worse for some people).
• Ergonomic mouse (currently, Logitech MX-500)
• Goldtouch adjustable split KB
• A decent task chair w/o arms (or w/ arms I can lower significantly to simulate their absence)
• WorkRave to enforce typing breaks

Orgs are usually already on with a good chair, so the expenditure is rather low. The only objection I've ever had is the monitor, and then they've always been willing to let me bring my own. Yeah, I shouldn't have to do that -- but spending $300 on a decent monitor is better than having headaches every day.

I actually get more done with the enforced breaks, because my typing speed stays higher on average than without the regular breaks (because of discomfort in the wrists and fingers). I say, if you have the ability, you should definitely institute an anti-RSI policy.