Looking for something to keep my son entertained.?

Lately my son has lost interest in his toys. He lost interest in his bouncer when he was about 4 months. He now has a exasaucer, jumperoo, and play mat. He would play and play in them when we first got them. Now he wants nothing to do with them. He will play for a few minutes but that is about it. Any ideas of what can keep him entertained? I just hate the idea of having to go buy another baby toy since they can get expensive fast.