Our school invitations are ugly, ugly, ugly. The cheap price does not make them worthwhile.
My daughter wanted something nicer, so we ordered from Pear Tree Invitations online (if that's not the exact name, you could still find it). I was very pleased with their choice of designs, and the items arrived in less than a week. She has several pictures on the invitations, and the quality was excellent. They weren't cheap, but I thought the price was fair -- including shipping, they were less than $2 each.
We were also pleased that this allowed us to create our own wording. With one item she invited people to her luncheon, the graduation ceremony and told where she's going to school next fall.
Before you order anything, you should find out whether your school does invitations or announcements. Some schools -- those with limited space -- are able to give their students a limited number of tickets, and in those situations you might actually need the official school items. This wasn't an issue for us; our graduation's held in a large, indoor facility and anyone can just walk in.