From your home-screen.
Go to System Settings->Accounts & Settings (or something similar depending on your OS version & phone).
Click on the name of your corporate account.
Uncheck "Sync Contacts".
Even if you do this, the corporate contacts that have already synced may remain there. If so then you have 3 options:
1) Delete each contact 1 by 1.
2) Go into System Settings->Applications->Manage Applications-> All, and then find your "Contacts Storage" app and delete the data. Unfortunately that will delete ALL of your contacts but any of your cloud-based contacts (on Gmail, Hotmail, Facebook, etc.) will automatically re-appear within minutes or hours (depending on your connection speed and contact count).
3) Leave your corporate contacts synced (taking up memory) but don't display them if they irritate you. Whether or not you can do this, and how you do this, depends your contacts app. On my phone with my stock Android contacts app, from the main screen of the contacts app, in the "Contacts" tab, I hit the settings button and then hit "Display Options". Then I select the account and check/uncheck the email groups.