Allow Enable Anonymous Access In SharePoint 2010 Sites

1. Open SharePoint 2010 Central Administration, Go to Application Management -> Manage Web Applications.
2. Select Your Site which you want to give anonymous user access and click on Authentication Providers icon in the top ribbon bar.
3. Click on Default Zone. Check the Enable Anonymous Access CheckBox and click on save.
4. Select your site and click on Anonymous Policy Icon In ribbon.
5. Select Default Zone from dropdown and select the permissions option you want to grant to anonymous users Selecting "None - No Policy" is recommended.
6. Close Central Administration and open your site collection for which you just had set anonymous access,   in browser with administrator account.
7. Click on Site Actions -> Site Permissions.
8. Click on Anonymous Access Icon on the top ribbon.
9. Select Entire Web Site Option and click on OK.

You can see the video tutorial by following the below link :
http://www.youtube.com/watch?v=RIxjKImNLUQ