What is the best, most straightforward way to make one’s ISP address anonymous. Since it may influence the answers and the mods, I should point out I’m not considering illegal activities.
The simplest way is to use one of the many free anonymous proxies out there. (I won’t link to any in case the mods decide this thread is a nono but Google is your friend.)
Be aware though that the connections will be slower, sometimes quite noticeably, as you’re channeling everything through another site. Also this is not absolute anonymity, the proxy site logs your IP (I don’t even know whether true anonymity is possible) so don’t do anything naughty! 
There is no way to make your IP address anonymous.
You can add a layer of indirection, though, by using an HTTP proxy service. If you need more than just HTTP, you can investigate a lower-level proxying system like Tor.
As mentioned in the OP, no significant naughty is planned. I’m not even going to mess with my Nigerian friends.