Another option…
Mapyx will launch a version of Lowrance Endura GPS in June:
http://www.mapyx.com/index.asp?tn=shop2&c=357
I've read a few bits about the Memory Map unit on Outdoorsmagic and I was a bit put off.
From my reading around, I got the feeling that the Garmin weakness is that whilst you buy the OS maps for the GPS unit, there's no way to use them on a PC for route plotting. Hence you'd either pay twice for the maps (eg Garmin + Memory Map / Tracklogs / Mapyx etc) or use one of the free online services.