Cant make my mind up about lenses.

I'm trying to figure out a set of lenses/upgrades.

Currently I've got 17-85 IS USM and a Nifty fifty (sold my 35-350mm recently because I didn't really use it all that much).

Now I'm trying to figure out what to upgrade with.

From reviews and short use I like the 24-105 f4 however as I'm going to be getting a 70-200 f2.8 is in the future, should I go for the 24-70 f2.8 for the little bit extra. Price difference is less than £100 so it's not going to be an issue.

Also on the same note with the 24-70 f2.8, is there much difference between the Sigma and the Canon Version. I've seen both have issues with flare, but then all lenses will have that issue at some point.

Opinions will be much appreciated.

The 24-70 vs 24-105 issue is the most thoroughly chewed bone here at POTN. It boils down to this:
If your shooting style puts more value on a faster lens than on one with IS, get the 24-70; if IS is more important, get the 24-105.

Are you sure you don't want the 17-55/2.8 IS instead of either?

Good point, I'm gearing towards EF lenses. So the 17-55 is out, it's also a little short for my tastes.

I suppose for "freezing" action the 2.8 is going to be the better bet because the light level has to be pretty low for the need of IS.

24-105 is nice for the extra range in a single lens, also means there's going to be some crossover from the 70-200.

Oh decisions, decisions, decisions.

If you sacrifice some AF speed etc and go third party you could instead get a couple of lenses for different uses. For example Tamron 28-75 F/2.8 and a specialised lens of some type, maybe even a fast ~20mm prime.

Your 17-85IS is going to be more similar to the 24-105IS then it is to the 24-70 f/2.8. If you are thinking of going full frame in the future, the 24-105 will have a thinner DOF, similar to an f/2.8 lens "looks" on crop. If you shoot in low light i would go right for the 24-70, 2.8 is more useful then IS on a slower lens. It would help to know what you like to shoot...

I have a very broad range of photography.

First there's my main work (part of my job anyway), this can be anything from studio work, pack shots, going somewhere and doing on location, generally always with flash to highlight the product. It's very rare that we don't use flash in some form. Although there have been occasions where I've needed a fast lens.

From a personal point of view:

Sailing
I'll be getting the 70-200 f2.8 is for this, although the wider angle of either lens will be good. Since I'll be on the water I'm either going to need a fast lens or IS due to waves, wind etc.

Sports events
Just took some shots of a friend running a 10 mile trail course with 1 mile of bog and mud, all in woods, cloud cover so had to use flash as light levels were quite low. Was pretty hard to take photos without bumping the ISO up heavily so resorted to flash. Also since it's running a fast shutter speed was needed.

Generally I know someone doing something so I end up going along taking photos of them.

There's general interest, sometimes I just go for a walk and see what inspires me, or even a drive.

I'm thinking of going full frame pretty soon. 5D MKII or if there is a MKIII coming out, i'd wait.

I've never been particularly happy with the 17-85mm often I've just stood further back and used the nifty fifty.

Sounds like you have a crop body right now. Buy lenses based on that not on what body you may get someday. Ef-s 17055/2.8 IS cannot be beat. Trade in your 50/1.8 for a 50/1.4 or, better yet, the SIgma 50/1.4. Yes, an EF 70-200 IS (I favor the f/4 model) almost completes the pix. Throw in an ext. tube and perhaps a 1.4x TC and you'll be busy for quite some time.