Just two nights ago I was talking with Luke about my idea for a "nested" system of ethical consideration. Today, I looked through James Hughes' Citizen Cyborg and discovered a chart for pretty much the same idea. I figured I'd throw it out there for you.
The idea is that there are different categories of rights, with each higher category including all the rights of those below.
Citizen. Definition: a person capable of advanced reasoning. Rights: consent, contracts, voting. Examples: adult humans.
Person. Definition: a sentient capable of self-awareness. Rights: "life, liberty, and the pursuit of happiness." Examples: children, great apes, dolphins, some other animals.
Sentient. Definition: a being capable of feeling pain. Rights: freedom from unnecessary cruelty. Examples: most animals, late-term fetuses.
Embryos, the brain-dead, plants, microbes, and some invertebrates are below the bottom of the scale and possess no rights at all as they have no interests to consider. Hughes calls these "property," but I wouldn't exactly say that a random bacteria is owned by anyone. The idea is simply that these things can be done with as one wishes without any particular moral qualms. The categories also line up fairly well with what are commonly called "civil rights," "human rights," and "animal rights," though where the lines are drawn differ from the traditional definitions of those terms.