Purplehel - Lots and lots of advice on the 'wannabe ultra runner?' thread a good, friendly bunch with a range of experience from tentative first thoughts about ultras to seasoned pro's with several 100 mile finishes.
Not sure what part of the country you are based in but a couple of suggestions from me:
The 'Dukeries Ultra' also in its first year (May 26th) with 30 and 40 mile options the route will be undulating but will lack the real gradient often associated with off-road ultra's. It will be good fast trails under foot for most of the route. The scenery should be good with it starting and finishing in Sherwood Forest. I have met the organisers who seem great and am in fact running with them and some of the other entrants on a course 'recce' this Saturday.
http://www.dukeriesevents.co.uk/
Second suggestion and my first Ultra UltraRace Peaks (19th August), a very well run event. No navigation required. Again some undulations and a couple of decent climbs but overall downhill profile. 40 miles starting in the Peak District and finishing in Derby City Centre. Again I have met the organiser Rory Coleman who is a top chap. The atmosphere last year was great a really friendly race. The time of year does mean though that it is likely to be on the warmer side, still the route takes you past a little ice cream hut .... never before or since has a mint choc ice tasted better.
http://www.ultrarace.co.uk/events/
That is just two from my neck of the woods, I suggest re-posting the question on the 'wannabe ultra runner?' thread for a broader answer.
Cheers.