Never, ever invite someone to the shower and not to the wedding and reception. This happened to me and several other people I know in a particular friends wedding. When the invites obviously went out and I didn't get one, I was so offended as were the other people. I know you probably feel that the B list people, if they end up getting an invite to the wedding, they should be included in the shower - but showers are really just for your closest friends and family anyway (and I'm assuming they are on your "A" list.)

Good luck and I hope this helps....