All rounder lenses are rarely good at anything - Jack of all trades, master of none - but they can be convenient to save carrying and changing a load of lenses. Personally I would not bother with such a lens.
To be honest your nifty should make a pretty good portrait lens as it is.
As for landscapes, ideally you'll be looking for a lens that cover the focal length range from around 10mm-20mm and I don't think you'll get much in that range for your budget. The best thing, probably, would be to get the new 18-55 IS kit lens, which will run you just over £100. IQ is supposed to be a step up from the old kit lens and you'll benefit from IS too....
http://www.camerapricebuster.co.uk/prod597.html
Another favourite upgrade, at low cost (but not as low as £200) is the Tamron 17-50 f/2.8. The advantage there is great IQ and the fast, constant f/2.8 aperture, but no IS...
http://www.camerapricebuster.co.uk/prod250.html
The bottom line is that a landscape lens should be wide and a portrait lens should typically be medium-long (around 50mm-85mm on a crop body) and have a fast aperture - f/2.8 or faster. The Canon EF 85mm f/1.8 USM would be a cracking choice, and an improvement on the 50mm but it is the wrong side of £200 and will not help you at the wide angle end at all. Basically, for £200 I do not see a worthwhile solution to your needs, other than getting the new IS kit lens for ~£100 to replace and improve upon your current standard zoom. Put the £100 you save towards a decent budget telephoto zoom like the 55-250 IS or a specialist (portrait) telephoto like the 85/1.8.
You cannot buy a lens on the cheap that will do wide and long and fast. In fact, you can't buy such a lens at any price.