You no doubt log into a bunch of apps and sites using your Facebook credentials, but you don't have to disconnect these apps to change what they're allowed to do through your account. There's a separate settings page where you can block apps from posting to your wall while allowing them to stay connected to your Facebook profile.
From the drop-down menu on the right of the toolbar on Facebook's desktop interface, choose Settings and then open up the Apps page to see all of the applications and sites currently hooked into your Facebook account. You can kick out any of these apps by clicking on the small cross icons to the right of each entry, but we want to just change their permissions (click Show all if you can't see all of the apps on one page).
Click the pencil icon next to an app and there are three main sections: The visibility of the app (and its posts) on your Facebook profile, the information the app can access, and what the app can do — you can edit all of these settings, though obviously if you limit the information provided to an app then you might break some of its functionality along the way.
In this case, we're interested in stopping apps from posting. If the app has requested such a privilege, you'll see a Post entry that can simply be unticked. Some permissions may have a "required" note next to them, which obviously means they're linked to the conditions of having the app connected to your Facebook account in the first place. If you don't want to (or can't) remove the permission to post, you can change the visibility setting at the top to Only Me, so no one else sees the updates on your Timeline.