The Battery Grip is nice!!! I have it on my XTi and it does make it feel better and never will I run out of juice. Getting Portrait shots of my 9 year old is easier with the extra shutter button on the grip. The 50mm gets extra work now
For Wide Angle lenses, I have the Sigma 10-20 EX and WOW!!!
I would look into the Sigma, built like a tank and I have gotten great pics. It comes with a lens hood and it's own carry pouch too. Trust me, nothing bad about it. I suck at technology but I will try to download some photos I took in Chicago. Stood in front(40feet away) of a 30-40 level building and I captured the top and freaking bottom. Nice!
Just curious, What makes you buy the 40D over the XTi? I know it is more durable and shoots faster, but what is it that makes you want to spend the xtra dough? I only ask because I may wait to see what comes out of this XSi that is coming out in April. I also may uprgade in the not too distant future and am looking for a more durable camera.