I have just been reading through this thread, I am using a GArmin eTrex Yellow (Linked to Memory Map on my lap top for uploading the cache position and occasionally navigating whilst I am driving) also 9 times out of 10 when I am out I have the relevant OS map with me as well (Lets face it nothing is more interesting than a map - I love them!).
I have been thinking about up-grading my GPS, is there one (at a sensible price) which will display OS maps?