I just ordered the Wacom Cintiq 12wx Tablet to help with drawing up my maps. I know it's not feasible to take into the cave, but it looks like it will work great to do the final cartography. The larger versions would have been even better, but with prices around $2000, they were a little pricey for me.
Here's the product info:
http://www.wacom.com/cintiq/12wx.cfm
I'll let you all know how it works out.