I don't mean to sound unhelpful cherokee, but you haven't really stated much in your requirements that hasn't been touched upon in the countless other threads advising on a DSLR purchase that you've probably already looked at.
Any of the budget/mid range DSLRs on sale currently would likely do what you need them to. They'll all have enough resolution print quite happily up to A3, and image stabilisation can be had either in the lenses available (Canon/Nikon) or in the body itself (some Olympus/Sony). The zoom factor is taken care of in the lenses. A good quality telephoto lens to go with whichever kit lens you end up with, will set you back between £200 and £350.
As for future proofing, I wouldn't worry about that. For starters, it's nigh on impossible and secondly a camera that takes good photos now will still do so in years to come. My Canon 30D is a 3-4 year old model and still does the job nicely. Getting a model above those in the budget range may help stave off the need to upgrade simply by having more features. It could be said that a DSLR is the most future proof type of camera to get as you'll always be able to use the lenses you invest in, even if you upgrade the camera.
For your budget I'd take a look at the Canon 450D, Nikon D60, Sony A350 or the Olympus E-520. All very capable cameras that are around mid-range in spec. The Olympus and Sony have IS built in to the camera. The Canon has IS in the kit lens it comes with, as does the Nikon (called VR).
Fact is, there's no definitive answer to your question.
All the current DSLRs are very capable and certainly a huge improvement over the point and shoot compacts you're used to. Sure there are things like availabilty and price of lenses/accessories to consider, but if a camera works for you then these things aren't a problem. Either personally or on here I know people using cameras from all the manufacturers and they pursue their hobby equally as well.
As often said, go and try to have a hold of the cameras you're considering as how it feels in your hands will likely make the biggest difference to your enjoyment in using it.
Also, when you get the camera, get a decent book on photography like
this or
this as these will help you get more out of your photographs than any amount of equipment.