Hi Steve,
I went throu' the same search for infomation back in March, and As usual "our friends" on TMA came up with the goods. Have a look at the following strings for their advice.
http://www.themodernantiquarian.com/forum/?message=187830&thread=17166
I ended up buying a Garmin Extrex Venture from Expansys
http://www.expansys.com/product.asp?code=110989
and TrackLogs 25k Digital Mapping program.
http://www.tracklogs.co.uk/cgi-bin/publ/user.cgi?obj=shopµ=as_shop_tracklogs&page=25K%20Site%20Centred
I've found that both software and hardware work well together and I'm well impressed with the accuracy of the GPS.
Hope this helps
RIV