http://checkout.google.com/support/bin/answer.py?answer=43205&query=Delete+Accounts&topic=&type=
If you aren't going to make payments through Google Checkout in the future, you can close your account. Here's how:
Sign in to your Google Account.
Click Delete all account info along the left side of the page.
Follow the steps to confirm you'd like to delete all information in your Google Account.
Once you close your account, you won't be able to access any information, including your Purchase history.
You won't be able to log back in to your Google Account once you've deleted it, so please be sure that you won't need to access any information in your account at a later date. Keep in mind that if you're a Gmail user, deleting your Google Account will also close your Gmail account.