Depends where you are. The best ride I've done within Fife is the Lomond Hills which start just above Falkland-
http://farm3.static.flickr.com/2268/2292599414_26f1f258d3_o.jpg
The route on the ground is quite hard to follow- just as you get to the peak, fork left up a very steep slope then traverse the hill to your left. When you see a track forking 45 degrees to your left back down the hill toward the reservoir, take that.
It's very "XC" but a lot of fun and I'd rather do that than Carron (though Carron is good).
Nearer the north, St Andrews and Cupar are close enough to ride to and around Kemback woods which just takes some exploring to be honest. There's a range of trails from XC to DH, but they're all doable on an XC bike (I've ridden the same trails on a hardtail with 80mm forks and the seat right up and my 6" AM bouncer and it's fun in different ways).
Pitmedden Forest apparently has good trails but I've never ridden them.
Tentsmuir Forest has a lot of Thetford style flat pumpy twisty singletracks that again take some exploring.
Laggan is about 1.45hrs North and is good, but on the way there's the Sidlaws by Dundee and superb riding at Birnham and Dunkeld within an hour of north Fife (closer than Carron).
GT and Inners are also within the same driving time as Carron.
If you need any more advice, e-mail me.