Mine have mainly been in Scotland:

WHW x 3 95 miles
Devil O The Highlands 43 miles
Highland Fling 53 miles
Two Bridges 35 Miles
Round Rotherham 50 miles

The Round Rotherham is suprisingly enjoyable and through such diverse areas, from the industry of the Don Valley to the fields around Roche abbey. Also very well supported.

The Devil and the Fling are also great races, and well organised. The Fling is ran so you can do it solo, with food bags left at every 10 miles or so for you. It's run by runners for runners so something like £10 to enter which is brilliant.

I'd recommend the Fling, The devil and the RR and then the WHW is a great race, and deserves its accolades as the hardest footrace in the UK IMO.