I am not familiar with either of those lenses, but I would recommend you do some extensive research before you buy a non-canon lens. Some tokina/sigma lenses are great, but a number are rather trashy.

My favorite all time lens is the canon 28-105mm USM, unfortunately you lose the wide end with the 1.6x crop factor. If you got the kit lens with your digi rebel (which is by all accounts a very nice lens), this would cover your needs. You could also consider the 28-135 USM IS - which gives a bit more range and has the very nice image stabilization feature.

I have the kit lens and recently purchased the 40-200 f/4 L. It is an awesome lens. Takes over where the kit lens maxs out. Great sharpness, contrast and color. Not very heavy. You wont be disappointed.

What is your budget? Do you want a long zoom to use in addition to the kit lens, or instead of?

see [url=http://www.photozone.de/active/survey/surveyform.jsp?filter="brand='Canon%20EF'%20OR%20brand='Sigma%20AF'%20OR%20brand='Tamron%20AF'%20or%20brand='Tokina%20AF'%20or%20brand='Vivitar%20AF'"&title='Canon%20EF%20(EOS)'#browse] this site[/url] for lens comparisons. It is the most complete site i have found so far.

Lenses come in 3 qualities (and price ranges) - consumer, advanced amature and pro. Pro is the canon L glass, and it starts at $600 or so and goes WAY up there. 4 or 5 grand or more for 1 lens.

your best bet is to buy the best glass you can afford, but you can always upgrade later. and new glass is always coming out, especially now with all the DC/Di digitally optimized lenses.

You need to do some research, and have a grain of salt ready. Recently I bought two lenses: I was looking for a 70-300 range zoom and a 17-40 or so wide angle fast lens.

I have a budget...I have kids, cars, school - lots of things competeing for my photo money. I hope to make some money on the side so I am choosing with that in mind...

On the wide end the choices are:

Sigma 18-50 2.8 $500

Sigma 17-35 2.8-4 $450

Tamron 17-35 2.8-4 $450

Canon 16-35L in excess of $1000

canon 17-40L $650.

The third one is rated almost as good as the last one. The second one is not very good. The 16-35 is WAY too much money for me. I ordered the 18-50...more range and faster than the 17-35. Nearly as good optically. Or is it? Who can you trust - users who defend their decisions, magazine reviews that might favor the manufacturer, (amateur) web reviews whom you have no clue of their test methods or agendas...you have to disseminate alot of info and then go with your gut!

Generally the long zooms (28-300, 18-200 these are 10X zooms) will lack quality at the far ends. It is tough if not impossible to get such a large range and quality too. The benefits are price or one lens for all. The best remembers quote i read on these was "The best way to turn your professional $3500 digital SLR into a point and shoot is to use one of these lenses".

I forget which brand recently got rave reviews (tokina maybe?) and the test shots showed such terrible barrel distortion, the worst i have seen outside a fish eye lens, I am no longer willing to trust much of what i read in teh magazines regarding lens reviews.

edit: new here, and the URL bit is not working..tried to edit to fix..no go. sorry.