Well why do you want digic 4 so much? if your serious about landscapes a used 5d will be of more use to you than say a new 500D, they seem to go for around £800 leaving you £200 ish on a lens which is a reasonable budget, it wont afford you an L lens but it should buy you something decent say a 28-105mm and perhaps enough change for a 50mm 1.8.
You will find that you get far more for your money second hand, if your set on the canon brand then google POTN its a dedicated canon forum that you will find to be a good resource when researching your purchase- it also has a fantastic buy and sell section; last year i purchased a 400d and 10-22 for £550 total, bargain
If you dont like the idea of used gear the 50d is a great camera at a great price, though whether it is due for replacement any time soon is anyones guess. I would recommend an XXD line over the XXXD due to the ease of use of the dual jog dials and the more robust grip and metal chasis. Dont be afraid of a kit lens, if you dont mind stopping the lens down and using a tripod its a fairly capable performer.
Best of luck with your purchase.