I mean free computers are nice but I don't know if I will have any use for them. any ideas?
I have no idea what a G3 iMac and G3 iBook are, but I say take them. You may find some cool use for them down the road, or just trash them if you don't find it.
Get yourself a wireless keyboard/mouse, hook up the iBook to your TV with PLEX, and use it as your media center! That's what I've done, except with the incredibly underpowered Samsung Chromebook.
Take them and do something stupid with them. They are PowerPC based which will make software support hard, but I'm sure something supports them. If it fails you could give them to someone with no computer or a shortage like MB said. Which is far less stupid.
Hell, send one to me and I'll do stupid shit to it. A fully functioning computer is still a computer even if it can't play Crysis 3 at 60 fps. Plus, a CRT is kind of cool these days.
Old computers have a following. Those are too old, but not too too old. Someone might be interested in them because they used them as a kid. I used an iMac G3 in my youngin' days in middle school so I have a soft spot for them. I doubt if I'm the only one. Someone might buy one from you just to smell 15 years ago.