Which Zoom

The siggie 70-300 is dirt cheap , check ebay i beieve they do some different models the one wtih the better glass is the one to go for.cant remeber if its APO or something like that in the name , one of me mates has one and its pretty damn good considering it was 80 quid 2nd hand

The sigma 70-300mm macro (1:2) APO is the more advanced version and does give an improved result over the 70-300mm macro (1:2).
However it is a dirt cheap lens in all respects (well built though - not L grade, but good enough) and I belive the canon 70-300mm beats it in quality.
I have noticed especially at 300mm, when focusing on further off subjects the sigma does degrade in sharpness noticably (past 6m or so) Its something to bare in mind
Further if you are using L glass now you will certainly see the degrade in quality with the sigma -

Can I ask , is there a difference between the Sigma 70 -300 APO macro and the Sigma 105 macro. Would the Sigma 105 be a better macro lens?

The sigma 70-300mm is not a true macro lens - its a telephoto zoom lens with a close focusing feature that allows magnification of 1:2 at around 0.5m - which is a deceptivly long mimimum distance. Its also what I would call a tripod macro lens - not good for handheld macro. Interestingly its 300mm focal length (where macro activates - between 200-300mm) gives it a great background blur effect and the lens does very well as a plant close up shooter - giving good results in this area. ( I would say its this lenses fortae)
insect example:
link

The sigma 105mm macro though is a true macro prime lens, so it has serveral advantages - firstly it is true macro, which means 1:1 magnification; further it has a much closer working distance, small and fiddly, but truer; in addition as its a true macro prime lens is it far sharper than the 70-300mm which is a budget lens. The quality of this lens is also on par with the canon 100mm macro.
Example:
link

note not fishing - can change to photobucket links if required

If you are serious about macro then nothing beats a good macro prime lens - though I would go for the sigma 150mm macro personally, as this lens will combine with both 1.4 and 2 times teleconverters from sigma to deliver a longer focal length (with corresponding smaller depth of field - very fiddly) with the increased background blur effect.
I belive the sigma 105mm will work with the Kenko teleconverters, but it will not work with the sigma edition

Sorry - only the sigma 70-300mm here - might want to wait around till 5-6pm for the those with jobs to get in I am sure we will have some users of that lens on the site!

Not personally or on my own camera, but I briefly handled it on the camera of another photographer and was quite impressed. Handles well, is relatively small, and the other photographer was very happy with it. But do read this review as well, because the reviewer clearly suggests you might be (almost) just as well off buying the other Canon lens.

Edit: Oh, oops, I thought you meant the DO. You didn't. Well, in that case the review is in your favour. Relevant review here.

In the review of the lens you mention, I quite like the statement that it's almost a hidden L Lens.

I have this lens. for the price range it performs well. It is a long way from L build quality and also lacks the performance at extremes of an L ie wide open and/or 300mm. It doesn't get a lot of use by me as I'm not a long focal length fan. Benefits are it is light, and a lot of range and IS for your cash, IQ is certainly on par with it's cost.

I'll PM you some shots in my folio that are taken with it.

Highjacker!! whats I.Q. mean?

Intelligence Quotient, as it is a sharp lens

Cheers , bloody obvious really