...the Sigma 70-300mm f/4-5.6 for my 400D. I've only used it once so far and the World Series by Renault at Donington Park. I'm impressed with it, but then I'm new to this, so was wondering what the general consesus is on Sigma and their equipment?

All help and thoughts greatly recieved ;)

It gets very good reviews for a budget Lens, in fact so much so I sold my old Canon 80-200mm and bought the Sigma, its the APO DG 70-300 with the red stripe, cost less than what I got for the Canon :D

under 70 quid plus shipping from Hong Kong, arrived 2 days later, bargain

Good lens, bit of a bargin buy. I only replaced mine when I got a (sigma) 70-200/2.8.

Short answer, polarised: Some folks will tell you if it's not OEM (Canon/Nikon)it's not worth having. Some will swear by 3rd party.

Personally, I think it's a matter of economics, and diminishing returns, with each step up you gain a little performance, for a lot more money. It's largely a matter of what you feel it's worth. Most of the 3rd party options are pretty credible these days.

Some of the Sigma Wide Angles are getting very good reports too along with the Tamron's for being incredibly sharp lenses

I recently bought the Sigma 24-70mm f/2.8 EX DG MACRO at my local Jessops closing down sale for £116 reduced from £289. That's a no brainer at that price. The pictures i've taken so far are sharp and punchy.

The consensus from various reviews are that wide open these lenses aren't quite as sharp as OEM, but then they don't cost nearly £900.

I've got various sigmas and am happy with them. They may not be white or have IS fitted, but they're a heck of a lot cheaper than Canoink lenses.

I've got the 10-20 from Sigma and am very happy with build and performance. I also rate Tamron as a third party manufacturer. The 17-50 is outstanding for the money.