At the minute, I'm liking Panaracer Rampage 2.35" a lot. They are excellent candidates for ghetto tubeless conversion too, as they seem to have good un-porous sidewalls and they hold pressure well even before you add sealant.
Rampages are nice but probably too much rubber for a bike like the IF, I run them on my Heckler. For an all round reasonable price and weight I'd go 2.1 Kenda Nevegal rear, with a stick -e Blue Groove on the front, fierce traction but still roll pretty quick.
If you want to splash the £ the Nobbly Nicks are great in the dirt but you'd be wanting the reinforced side wall ones if you're riding rocks. Also if you want some speed in summer get a set of semi nobblies as well, I run Kenda Small Block 8s in the dry (Maxxis Larsons are similar) and it turns the bike into a rocketship
Standard fit on my Kula and have been very impressed by them. No qualms about running modern rubber on my bikes as they are all riders. I will be putting these on the CB in the very near future as the sidewalls are gone in the Wildslippers.
Tyres and Saddles are two things that I think have defintely got better rather than worse.
For the worst muddy conditions I'd also vote for Panaracer Trailrakers, although if you have to ride on the road to get to the trails you will find that they can squirm pretty horribly in the corners.
For all other times I would say High Rollers, but go for 2.1's, NOT the 2.35's - They are completely different tyres in terms of performance. The 2.1 rolls fast and feels light and responsive, but the 2.35 is heavy, turns slowly and feels like you are dragging an anchor!