24-70mm f/2.8L.
I the 24-105 is one of the best walk-around lenses available for the Canon. IMHO, however, the 24-70mm is THE best everyday lens you can use. it's very versatile and can be used in almost any situation. it'll definitely give you that background blur you've been wanting.
Also, get the 10-22mm ultra wide angle to get amazing shots like ///M PWR 00 posted. that's definitely next on my list! that and the 70-200 f/2.8L IS.
