[Dabhand16]

Aaahhh. A little more detail always helps. I presume your kit lens is the 18-55. Your budget is going to be the biggest influence. I wonder if your initial selection of 28-135 is trying to get one lens to 'do it all'. If so, the 18-200 range is generally accepted to be the best all round range.

For portraits, a good focal length is 50-70mm. With your 400D this will equate to 75-105mm in 35mm terms. Landscapes benefit from wider angles.

Suggestions - the 'nifty fifty' f1.8 is a superb lens and will be great for portraits. It is fast, and will enable precise control of the depth of field. The best bit about this lens is that it is CHEAP! £60 at One-Stop digital, or About £75 from Warehouse Express. You can then use the kit lens for landscapes and your long lens is already in place.

If you have a bit more to spend, and you want a zoom that covers portrait and landscape consider the 24-85,17-70, or 28-105 or 18-200 ranges. These are covered by Canon and Sigma.

I'm sure now that you have given some more info, other members will chip in with their opinions.