Choosing my next Canon lens

Need lens-buying advice from Canon photography nerds.

The Mrs. and Me are starting to really dig taking photos again – she with a Rebel XT and me with a 30D. We currently share joint custody of 1) the XT’s standard 18-55mm zoom (blech) and 2) the glorious and much-loved 50mm f1.4 (yay!).

So, let’s say, hypothetically, a fella wanted to pick up a new Canon lens to add to these two cameras’ modest arsenal. If we wanted a fast, flexible lens (that would mostly get used for baby picture-taking), what would you guys recommend? Possibly a higher-end, faster zoom?

Canon L Series 24-70mm f:2.8

No question at all. Ridiculously fast – you get the 2.8 option across the entire zoom range. Unbelievably sharp at 5 and up, but enough DOF to give you some great control.

Downside: cost. $1,050 to $1,400 or so.

Somewhat acceptable option: Tamron 28-75mm f:2.8

Also very sharp at 5+, also flexible 2.8 aperture available across the zoom range. Build is very good, but nothing beats an L series. Significant advantage is cost at $370 or so.

Most wedding photographers who shoot Canon use the L lens. Us mere mortals use the Tamron.