A hook for admin post and edit pages?

I need to set up WordPress to add some different meta information to all posts, I was wondering if I can add some form elements into the write post/edit post page so that the user doesn’t need to manually type the information into the custom fields (some will be drop downs with specific options)
I searched for a hook for those pages and didn’t find any, but I was wondering is perhaps any undocumented hook or any other method exists, besides modifying core files (which I really don’t want to do)
Thanks in advance.