If you want a nice simple easy to fix vehicle for a reasonable price get a good second hand Discovery Tdi, one of the late ones for preference (they stopped making the Tdi in mid 1998), nice and stable for towing. Any serious problems will most likely long since have been fixed. Autos are good in one way for towing as they are smooth, but I think they are a little short of puff with the Tdi engine (and the Td5 for that matter) others disagree and you can always uprate it with a bigger intercooler and fuel pump tweaks anyway, not that expensive. The higher spec ES ones aren't really much more complicated its mostly just leather, fancy wireless, twin sunroofs, that sort of thing.
Later ones 1999-2004 with the Td5 engine are also good, I run a 2002 4.0 V8 auto (same vehicle except with the V8) which is wonderful to tow with but a little hard on the juice ... I love it though. The later ones are more reliable on the whole and the roadholding is certainly considerably better.
Discovery 3s are too new to think about IMHO, too much electricity to go wrong and I wouldn't consider one for at least another year. I'm not even sure if I will consider one then -- I'll reserve judgement until I see what else goes wrong!! There's nothing wrong with many of the Japanese 4x4s, I just don't like them because most of them were designed by somebody with a bag over their head. A Landcruiser Colorado (Prado) would be a good alternative but I don't know much about what to look for on those.
Regardless of what you buy, if possible get one without a towing hitch, because if it has towed all its life the transmission may be a bit tired by now. Basically they are mechanically sound if properly maintained but the single most important bit of advice I can give is to find somebody who knows Discoverys from top to bottom and get them to come and look at anything you are buying and test drive it. A lousy driver who has no mechanical sympathy can do a lot of damage to a Land Rover transmission over time with rough gearchanges etc.
If you want to find the Land Rover equivalent of RIBnet go and look on www.lr4x4.com
it is an excellent forum (though I could be biased as I am one of the moderators...) lots of friendly people and a staggering amount of collective knowledge about anything with a green oval on it