The one I've always used belongs to MCI. You dial 1-800-444-4444 and it says, "Thanks for calling MCI! We see you're calling from xxx-xxx-xxxx..."
I actually pay for the ureach.com service for my job and works pretty good as an ANI. The only thing is, they have to leave a message for you to see their number. The cool thing about ureach.com is that if someone is calling your home phone using *67 all the time and you want to know who it is, just forward all your phone calls to your toll-free ureach.com number! *67 is useless against ANI, as long as they leave a message you'll get their number.