favorite "walk around" lens?

Another vote for the 17-85 IS.

For shooting in the close-up to not real far zone its versatility is wonderful.

Never tried one, but from other's reviews the Sigma 17-70 sounds like another good choice to match with your 70-200/4.

Don't forget to budget some money for a decent flash. Sigma 500 Super or Canon 430EX for ~ $200-$250 is a great starter solution.

35 f/2, 28 f/1.8, 17-40 f/4.

70-200f/4

I'm tempted to say my sigma 24-70, but I think practically speaking it has been the sigma 18-125. It's just that now that I have the EX, I want to use it more because of the gorgeous pictures it takes.

I went for the 17-40 L as my walk-about lens. the focal range suits me as i prefer wider to longer as a main lens. I hardly ever wish it was wider, but occasionally longer would be nice. But i chose it for the build quality and image quality as much as for the focal length.
I was also interested in the 10-22 but felt it was too extreme to use as a walk-about lens, so would give less value for money for my needs.
The 17-85 IS appealed at first but I read a lot of less-than-complimentary reports about this lens - seems a bit of a lottery - so I decided to go for my 17-40 and so far have no regrets.