Sounds like you do pretty much what I do. I have a bouncer for Bosley and change the toys on it and his gym regularly but he doesn't seem to have a favourite yet. He loves music - whether I sing to him, or he has the music in his bouncer on, or if I have a CD playing. I know that music and sounds are supposed to be great for them. I sometimes worry he'll be bored, but then I think I am thinking that if I were him, I'd be bored! He finds the littlest things fascinating and he'll grizzle if he's had enough or doesn't like something. When we're playing on the floor, he loves watching my hair flop around. And he loves it when I wave my finger and touch his nose and say 'beep'. And lately he's loving watching me eat. And he likes it when DH and I open and close our hands or clap. See, easily pleased!

Tummy time isn't such a success though....