I'm glad you're upgrading from the kit lens, though Canon's kit lens really isn't too shabby. You'll see for yourself when you make your own comparisons to whatever you decide to get.

I have no experience with the Tamron lenses, but I do like the quality/price/value of the Sigma lenses. That f2.8 is going to be a big help in any low-light situation.

But I have a special place in my heart (and my camera bag) for the Canon Image Stabilized lenses and the 28-135mm USM IS is the everyday lens for my own camera. I'm completely sold on Canon's IS system. It's enabled me to get low-light shots which would be impossible otherwise, and to free me from the tripod for many others. I'd give a serious look to the Canon lenses - even if you can't afford (as I can't) the spectacular EF 70-200mm f/2.8L IS USM

Here's a forum of user reviews for the Canon EF-S 17-85MM f4-5.6 IS USM. It's a well-liked lens, but the forum lists 162 reviews so you get to see all the gripes about it too.

Here's the review forum from the same site for the Sigma lens. Unfortunately the Tamron you're looking for isn't listed there. Fred Miranda's is a good site though and features real-world reviews from people who've actually bought and used the equipment.

Well you asked for thoughts and you now have mine. In the end, the decision is yours though - and so is the enjoyment of discovering the capabilities of your new lens. Have a great time and let us know how it works out!

Thanks for the input, Chip. I went down to B&H and checked out the Sigma 18-50mm f/2.8, Tamron 17-50mm f/2.8 and Canon 17-85mm f/4-5.6 IS. I preferred to have a 2.8 lens to allow use in low light at faster shutter speeds, and this factor pushed me towards the third party lenses. (Canon also offers a 2.8 wide zoom, but price is prohibitive.) I purchased the Sigma and tried it out this weekend. I am very pleased with the results. My only criticism so far is that the lens adds quite a bit of weight to the XT, but that may be inevitable with any 2.8 lens - more glass and less plastic than the kit lens.

They're all going to be heavy; it's just something you grow used to. My 28-135 weighs considerably more than the XT.

That Canon "L" glass is always going to be expensive. It's possible that you might be able to rent one either for a special application or just to try it out. That's a long shot though; I know I can't rent them in my area.

You can always look at it this way: the Canon 16-35 2.8L may run $1,400 but that looks like a bargain compared with the 400mm 2.8L I'm currently lusting after...

I'm really impressed that you could just pop on over to B&H. There's really nothing that beats actually holding these things in your hand before you lay down the dollars. It's probably best that I can't do that or I'd have to load another mortgage on the house.

At any rate, congratulations on your new Sigma. Post an image or two and have a great time!

i just bought the 28-135 is usm cannon still getting use to it but found that it blured alittle when using it for action multi frame shooting unlesss could\ it be the operator? I am also picking up the 70-200 is L4 f4 see how that shoots.

chip doc so am i but alsa it is a dream for a 400mm L4 2.8. although the store i shop at just sold a 2.8 L4 for 6,000 canadian. way out of my bracket and my abiltity.