Map and compass for me - never occurred to me to spend any money on a GPS. My navigation skills aren't amazing, but they have been good enough to get me out of a fair few white-outs and other tight spots in the past.
Unless I am trying to navigate in poor conditions, I don't tend to look at the map much beyond working out where to leave the road. Have been caught out a few times in areas with lots of paths/forestry tracks. I think this is where I'm most likely to get lost!
I suppose GPS would have assisted me in getting to all of the summits I had originally planned in cases like this day out in the Cairngorms
http://www.walkhighlands.co.uk/Forum/viewtopic.php?f=9&t=3440, but in those conditions I prefer to simplify or cut short the route.