How to turn off syncing to gmail, calendar, & contacts

Theres a free app on the market called AutoSync Account Activator that lets you select sync time intervals for all of your accounts. I'm sure you can use this to completely disable their sync. You can also use it to sync over wifi only. Make sure that your contacts application uses its own database though. Many contacts apps are still using the google contacts database and therefore still need the sync functionality. If you are not sure, try to create a new contact in the google contacts app and then see if it shows up in your 3rd party contacts app. If so you should leave contacts sync at maybe a 24hr interval.
And if you are concerned about numbers syncing with your google account there is an option when you create a new contact whether you want it associated with your gmail account or just have it stored on the phone unsynced.
Thanks Eric S!

You're absolutely right, I couldn't see the checkboxes because I turned off Automatic Sync. Now that I turned on Automatic Sync, I could see all the checkboxes and disable sync for all accounts. HTC Desire HD doesn't seem to have Power Control widget, all these settings are done through Accounts & sync. Let's hope it works as expected!

Indeed, the data should not have been syncing with my Google account when the Automatic Sync was turned off. But, it did sync data with my Google account and leave me with a splitting headache trying to work out how to stop it. Thanks again!