I will be buying the canon 50d, and since i sold all my camera lens (need it the money at the time),and I don't have a lot of money to spend.I can only get 1 lens,I will be shooting the following, outside construction photo's and landscape, some flowers and birds.Inside picture of my daughter and son. I had L lens and that's what I want. But only 1 for now, in few years hopefully i can buy more. I was thinking, 17-40L, 24- 70L, or 135L. Thanks for your answers
Based on your requirements on a crop camera I think only 17-40 fits your bill, apart from much more expensive 16-35. I think you would find 24 not wide enough for shots inside and outside building shots, but that depends on your shooting style. When I used to have a crop camera I have chosen 17-40 as the first L lens due to it's price and range. Never looked back.
Edit: forgot about birds and flowers- 24-105 would probably be better than.
To me this just isn't a one lens solution. Construction and landscape sounds like you want some wide angle coverage. Flowers you probably want something that can shoot fairly close up. Birds you will need something with a fair amount of reach and taking pictures of your kids indoors you will probably want a fast aperture. From the options it would seem you have about $1,000 to spend. I would spread that across at least two lenses. If you have to get an L, the 17-40L would work reasonably well for your construction and landscape shots, and is less expensive allowing you to buy a second lens. A 50mm f/1.4 would work reasonably well for indoor shots of your kids and with extension tubes could do flowers pretty well too. With your budget you will have to add a lens for birds later. I hope this helps.
If I was limited to the price of one new L, I'd give up on the L and investigate some of the fine non-L options. For the 1,300ish price of one new 24-70 you could pick up a nice used kit off the b&s here. Say a Tokina 12-24, Sigma 50 1.4, Canon 85 1.8 with several hundred left over. Oops that sounds like what's in my bag.
You might also want to consider the 35 f/2 or 28 f/2.8 and the 70-200 F/4L. You have a good low-light wide angle and a decently long telephoto zoom for birds.
