I'll say this much about zoom's : the cheepest one worth having for me, is £800.
The only zoom lens i've ever used professionally has been the 70-200 2.8 L IS, which is £1300 or so (not what i paid ;) )
With fixed/prime lenses, you gotta take that 1.6x crop factor into account. Basically take the MM, say 50mm and multiply it by 1.6, so that makes a 50mm's effectively and 80mm lens, which is good for portraits as i'd use a 85mm lens on a full frame camera.
The 35mm F/2.0 would be the closest you could get to a '50mm' range, it'd be 56mm. Sigma also do a 30mm lens for digital only camera's but i've never used it.
Of course this is all going a bit advanced and probably more than most people require but anyone who's getting into photography in any semi serious mannor will have a few prime lenses in their kit bag.