I don't know what the 15-85 costs, but if you think you might want more on the long end, you might look at a Tamron 18-270; I love mine.
The Tamron 18-270 PZD is a very useful lens. I own one (well...I gave it to my son), but its not in the same league as the 15-85mm with regard to IQ, focus motor, IS, and build. The Tamron also does not have a damped focus ring or FTMF. Its VC is loud and jumps around in the view finder much more than the silent Canon IS, and the PZD focus motor is much slower than the Canon's USM motor. The Tamron sells for about $450 and currently there is an additional $30 mail in rebate so its a very good value and I recommend it. The Canon 15-85 sells for between $700 and $800. A hood which for Canon, which is a fee standard accessory with the Tamron, costs an additional $30 or so. Still I gave up the Tamron to my son when I got the Canon, and have never regretted it. Its a better lens in every respect.