You can discuss walkabout lenses until you are blue in the face. Some people prefer to carry around bag full of prime lenses (fixed focus lenses incase OP is not familiar). i.e. 20mm, 28mm, 35mm, 50mm, 85mm, 135mm, 200mm. Others prefer lenses biast towards the longer end of focal range like the 28-135mm. That's a good lens to be honest. I've used one and it was a really nice lens for walkabout. Having a walkabout lens that goes from 10mm - 200mm simply does not exist, and would defeat the purpose of an interchangeable lens system. If you think/find you take shots within the range of 17-50mm, then you could look at:
Canon Kit Lens IS version
Tamron 17-50mm f/2.8
Sigma 18-50mm macro f/2.8 (discontinued/can't buy new anymore I don't think)
Tamron 17-50mm f/2.8 VC
Sigma 17-50mm f/2.8 OS
Canon 17-55mm f/2.8 IS
(VC = Tamron Image stabilisation, OS = Sigma image stabilisation, IS = Canon Image stabilisation)
They go up in price as you go down the list, but not necessarily in quality. For example, the Tamron f/2.8 non vc is widely considered to be the best walkabout lens for crop camera bodies in terms of bang per buck, in that it is affordable and yet tac sharp for the money, rivaling even the Canon 17-55mm. Most people will compare to the Canon since it is hugely expensive and generally considered to be of L glass image quality.
Having said the above, I had a copy of the Tamron non VC and it was awful. Literally, awful. I sent it straigh back to the seller and to be honest, I found the whine of the focus mechanism very annoying. It's very loud in operation, more so than any of the rivals in the above list and can intrude and draw attention at certain situations.
The Tamron non VC is generally considered to be less sharp than the non VC, and people find this unacceptable given the added price so it is not a popular lens at all.
The Tamron lenses do feel cheap in build, but most find they hold up ok.
The Sigma 18-50mm f/2.8 EX DC Macro is a good lens and often overlooked due to the popularity of the Tamron. Its zoom ring rotates the same way as Canon lenses do (i.e. clockwise zooms out) which is nice not to have to re-learn/re-teach yourself which you tend to do instinctively if you are coming from a Canon background. The build is very high quality and better than the Canon (read why below) and it also features the added benefit of macro functionality with a very close MFD. Not a full on macro lens, but still pretty handy to be able to never have to worry about stepping back to achieve focus as sometimes you can nearly be touching the front element on a plant and it will still focus.
This lens also has an issue though...it's made by Sigma. The quality control seems to be just as much a lottery as with other 3rd party lenses like Tamron, although people do still have issues with Canon lenses to be fair. I went through 2 copies before finding one that was good. First had a decentering issue, and second backfocused. Depending on copy and focal range, it matches the Tamron 17-50mm f/2.8 in Image quality (IQ) and performance, other than to say the Sigma is built better and not noisy in AF operation.
The newish (out about a year ago) Sigma 17-50mm f/2.8 OS is Sigma's replacement for the 18-50mm lenses and introduces OS. This lens is MASSIVELY overlooked, as people at this price point start to realize that they are not that far away from the price of the Canon 17-50, which is commonly perceived to be the holy grail of walkabout lenses on crop. However, the Sigma 17-50mm OS is a fantastic lens. It just doesn't have much support mainly due to the success of the Canon. This lens OUT PERFORMS the Canon in terms of center frame IQ quite noticeably. It is built better, lighter and costs still a couple of hundred pounds less. At this price point though, we are talking a commitment and really a top end piece of glass for crop.
So why shouldn't you buy the Canon and spend £750 on a piece of Canon non L glass? Well you can. It's just that you might want to consider some of the above 3rd party lenses for bang per buck. If you do however want the best, and you can afford it, and you need top IQ WITH image stabilisation in your arsenal, then my advice is to decide what is most important to you. If you MUST have the absolute quickest AF, and do not mind the extra weight and prefer overall entire frame sharpness and contrast, get the Canon 17-50mm f/2.8 IS. If you prefer to save a couple of hundred and want better build, slightly lighter/smaller lens, acceptable AF, better center sharpness and 3 year UK warranty, get the Sigma 17-50mm OS. The Canon's build is not that bad, it's just a lot of money for a non L glass lens and it has an issue with dust getting inside. A lot of people have this problem with this lens.
There are also Tokina lenses to look into which I have no experience of. Really, if you are upgrading you need to ask why am I upgrading. What to I require that will aid taking better pictures. Look at whether IS would help you and your style of shots. Do you need better IQ? Budget. What focal range suits. They are the main key things. You can have the best setup worth thousands, but if a walk about lens that is longer gets the shot and a 17-55 range lens doesn't, it's worth nothing.
Hope this helps. Sorry it's long and I typed it quick without checking spelling.