Shanethemill,
I have the 17-40 "L" as well,. and indeed it is an excellent lens,.... ( do you sense the "but" ? )
DoctorCarla,...
....this wide angle lens is not the best solution for portraiture. In fact for the price of the 17-40mm "L" you could buy several lenses that would all be more suited to portrait work.
The Canon 50mm f/1.8 is a must!
At a mere $70.00 or so U.S. dollars it is the best deal in lenses going. And as Jeppe says with the 1.6 conversion it will equal a perfect 80mm (which is within the range of recomended portrait lenses, ie: 80mm-135mm)
Another very affordable lens that is specifically designed for portrait work is the Canon 135mm Soft Focus. It sells for under $300.00 (I think about $250.00? ) and the soft focus (which is an optional setting on the lens, it is normally tack sharp) with the soft focus setting you can do wonders with those soft baby photos.
For more flexibility, look at the Canon 28mm-135mm IS.
Although not the "perfect" portrait lens,. you will love the flexibility of this lens with its wide zoom range,.. much of which happens to be right smack dab in the middle of "Prime Portrait" zone (80mm-135 again
) but it wil also allow you to do group shots and landscape photos among others. It is NOT the best lens for indoor work without a flah though. (it likes a lot of light)
Now if you like wide angle landscape photography and group photos,. then the 17-40mm "L" is the one to get! 
But for the price of this very specific use lens,. you could purchase all three of the lenses I mention above and have the beginning of an excellent kit.