depends on your shoting style.it just like asking us to recommend u a piece of clothing without knowing who u are...
so, u like wides?or tele?and where do u usually 'walkaround'?
There's no real definition for a 'walkaround' lens, but to me, that is a lens that has a reasonably wide zoom range, is decently wide and zooms reasonably far. That would be things such as the kit lens (29-88mm effective), a superzoom (29-320mm effective) or say the EF-S 17-85mm (28-136mm effective).
If you're more into street photography and indoor portrait shooting, then the 24-105L is very nice. Not to mention that the IS will probably come in handy.
24mm at the wide end isn't all that wide though, so if you suddenly want to do architecture or landscapes, it might be a little limiting.