What should I do? Moms 50th Birthday?

Me and my older brother are planning a surprise party for my moms 50th birthday. It will be a formal dinner party with live band and a DJ. We already have the dinner menu set, eat invitee will have a choice of an entree and dessert. My problem is what the heck to serve them for appetizers. We don't want to do anything too heavy before dinner but I don't want anything too casual. Please if anyone have any ideas for a few appetizers, we are expecting at least 50 people, give me a few ideas. Thanks