Headphones with subtle music or just white noise.

Change your work schedule so you have quiet time before the office opens.

If you have some flexibility about being at your desk, you can find a lot of secondary spaces which go unused. Wiring closets, conference rooms, file rooms, storage areas.

First off - talk to your boss about perhaps working from home N days a week. There are other options - but they are all workarounds I think (noise cancelling headphones, etc.)

Short term, this site is helpful:

http://simplynoise.com/