"Something really special" and "all rounder walkabout lens/gigs/nature/portrait everything'
Are not compatible.
You can have a nice walkabout lens but it wont be good at portrait or nature.
Nature by itslef normally requires a 2-3 lens set up (wide, moderate tele and super long tele).
You need to think what you really want to photograph. Really I think you will need 3 lenses to do what you want.
Heres some options:
Canon 17-55mm f/2.8 IS: good walkabout lens, Ok portraits
Canon 15-85mm f/5.6 IS: Excellent walkabout lens, nice and wide for landscapes, a little more reach than the above, but not good for portraits.
Sigma 18-35mm f/1.8: Extremely fast for a zoom, extremely sharp. Limited focal length means it is not a great walk abut lens.
Canon 70-200mm F/2.8 IS: Great for nature and portraits, general walkabout when you want length.A little short fro wildlife but a TC will help a lot.
Canon 70-300mm f/5.6 (L): good for nature including wildlife life, cheaper than the above, but slwoer aperture limits appela for portriats.
Canon 85mm f/1.8: very cheap long portrait lens, too long for crop really.
Sigma 35mm f/1.4: Good portrait lens, might be a little boring focal lenth for generaluse.
Canon 10-22mm : great nature/architecture lens, OK walkabout if you like things wide. Works well with the 70-200/300 for nature. Useless for portraits
