Gee, remember that you are one person, and thus are presenting the views of a world seen by that person.  What you have seen in your views of the world are not necessarily the same views others have seen of that same world.  What we need to post in here are generalities, and ensure that we realise that we are all speaking from the view out of our own windows onto the world.  We do not have to agree, but we need to respect the fact that others may see something different out of their windows.

That being said... SandieG, look back at any job description you received, any details that would help you determine how to flesh out your position more.  Perhaps what Gee has stated is true, and this bossie will not take ideas from his PA.  Perhaps what Atlanta stated is true, and this manager hit upon the right time and place to present the idea to your boss, and that's why he bit on it now and not when you presented it.  You need to look out your window and see what the view is from there and make decisions based upon that.  If bossie seems the type who will never grow to use your skills, and you are this unhappy, brush off the CV and start looking.  Chalk this up to a learning experience and see if you can come up with questions that will help you during the interview process to keep from landing in a similiar situation.  If bossie seems like he might be able to be taught to see your usefullness, and it's a lesson you want to teach him, then stick it out and start that training.  Perhaps it is the way/time you approached him that caused the issue, if so, then teach yourself how to better choose your timing with this new boss.

Any ideas that are implemented, that you have had similiar, I would still talk to the implementors and see if your suggestions might not be able to be used to improve the plan/idea that has already been approved.  This way you are still showing your usefulness and skills, even if the core idea isn't credited to you.  Keep that up and soemone will notice and you may find your ideas no longer fall on deaf ears, even if those ears no longer belong to your current boss.

Good luck, and let us know what you decide to do.