Okay, I can speak specifically to this. It's not nice to talk about and a bit gruesome, but I'll speak about it frankly so apolgies if this sounds gruff. But believe me, this stuff is best worked out when you're still sane. Planning is so key. As an aside, there is such a thing as pet hospice- you can make a plan for comfort care as the last days arrive as well. having pain medication or a sedative on hand can be very comforting for both you and your critter. Dr. Tami Shearer is a bit of a forerunner in the field, and unfortunately no longer practices in columbus, but her website is useful. http://www.shearerpethealth.com/
With specific regards to cremation, my recommendation is Schoedinger Funeral Home downtown. They are very specific about making sure that they do one animal at a time. Other places may assure that you get your ashes by separating pets with fire bricks, kind of compartmentalizing the ashes, and like cookie said, you might also get a hodge-podge from other places. But I'm fairly sure that shoedingers is the only place that one pet per trip through the oven.
Other logistics: They can pick your animal up from your home. this is a little bit more expensive. They can pick it up from a vet's office, this is a little less expensive. Or, you can take the pet to them. I think for a cat, it cost about 80 bucks for the entire service- pick up, cremation, fur clipping, plaque, and wooden box, plus a certificate from the funeral director certifying its yours. Cost varies with body weight, as bigger animal means more gas + time.
Besides that, they were completely professional about it. They treated it (and me) exactly as if it were a human loss. They have a pet services coordinator who did exactly what she should. They coordinate a grief group if you want. They made this process as normal and trouble free as can be imagined. Never once did I feel less important for doing a pet deal there, and they were very sympathetic. http://www.schoedinger.com/pet_services.shtml
My sympathies to you. I hope you don't need this any time soon, but I applaud your foresight.