Having just flown a Raven I across the US, I found the GNS530 to be a tremendous help. It's hard to consult a paper map all of the time while sticking a helo around, and just having the various types of airspace (military, restricted, etc.) represented on the screen was very handy.
The 530 *is* a bit of overkill since it's an IFR approach GPS, but (if you get the full IFR panel) then the ship could be used for GPS approach training.
I personally also think that a helicopter should have an attitude indicator, just in case things go pear-shaped wx-wize too quickly. The high-timers might disagree with this assertion, but if I'm ever fortunate enough to buy my own ship I'll be looking for one with an AI, or else put one in.
Dave Blevins