[Quintin]

I'm still using the EF 18-55mm 3.5-5.6 IS that came with my 500D. Not a single photographer I've spoken to — whether amateur, semi-pro or pro — has ever had anything bad to say about it. It's got a decent range, especially for very wide shots, and the image stabiliser is great... not that it's that important on a relatively short lens. Kit lenses are apparently better now than they were a couple of years ago.

Of course, there's no contest between standard kit lenses and higher-end lenses like the L-Series lenses. These lenses have superior quality optics made from very high-grade materials; when you read their reviews online, you'll spot terms like "Aspherical Lens Elements", "Flourite Elements" or "Ultralow Dispersion Glass Elements", which means that you're getting the real deal. Higher quality glass means better images.

As for third party lenses like Tamron and Sigma: I'd say stick with Canon products. Third party lens manufacturers also use flourite and UD glass in their construction, but the lenses have to be reverse-engineered from the Canon lenses, so the quality that you get out of them usually isn't as good. Also, as far as I'm aware, you won't find Image Stabilisers, USM motors, or similar technologies on third-party lenses. I'm guessing it's either a legal or a technical issue, or both.

If you've got a super-steady hand and don't need an image stabiliser for telephoto shots, or if you don't mind a noisy AF motor, you might have a look at a third party lens. They're definitely cheaper. But I doubt you'll get as far with quality as you will with Canon.