In reply to Giles Davis:
Depends what you mean by 'trails' - they're not all the same. Most are flattish and grip isn't a problem, so an ordinary pair of road shoes - perhaps with a more robust midsole to limit 'rock-strike' on the feet - are perfecty OK. If the terrain gets significantly uneven but still hard, then a low heal and some minor studding becomes more useful. If it's steep grass/mud then you will probably benefit from proper fell-running shoes, but then it's probably not 'trail' running.
I have Walshes, Inov-8 TrailRocs, Salomon SpeedCross and some Saucony road/trail somethings. Most runs are in the last of those (all largely off-road). SpeedCrosses come out if I know the terrain is flat and smooth (thin forefoot midsole, bit unstable) and my feet/legs are aching (very comfortable heel cushion). Inov-8 for long runs (light, grippy, good protection, stable but wear down quickly). Walshes if I'm expecting steep grass/mud and little hardpack (super grippy & stable, but no cushioning).
Short answer is... it depends on your trails and your feet (Shape? Prone to blisters? Graveyard of toenails?).
The only way you'll find out what suits you is to try some and see how you get on. Give it ten years or so and you'll have a pretty good idea which shoes - which of course are no longer available - were best for you.