I'm a paralegal by profession and part of my job is discovering useful information regarding people who are suing our clients. Much of that information is available to anyone willing to spend a little money and/or time on the project. This post will give you some resources in case you ever want to play PI, whether for geneological research, to learn about the family of or your kids' (or your) newest beau, or to learn about the family that just moved in down the street.
You can start with a simple (and free) websearch on Yahoo, Google and/or other search engines. Obviously that is more effective when researching uncommon names than common ones, but if you can find someone's blog or message board posts, or email list posts, you may discover a side of them you didn't know existed. Also able to be searched for free are websites like 411.com which allows reverse phone number searches (enter the phone number, discover the owner). Many sites like this give you a little information at no cost, and then offer to sell you more. I've bitten a few times, and have been disappointed more often than happy. One site I would recommend if you want to spring for a few bucks is Knowx. Their price list is here and it is very reasonable. They let you know before you search if the area in which you are interested is available and I've found their information to be reasonably up to date.
If you don't want to spend money, there is plenty of information available on the web, but not covered by search engines. Is the person you are researching a licensed professional? Do a websearch for your state's board of _____, filling in the blank with the appropriate profession (though doctors are usually licensed by the board of medical examiners). Some of these sites even list disciplinary action and/or verified complaints against a person. A listing of physicians can be found on the AMA's website. Does your subject own a business? If so, it may be an LLC or corporation, in which case it will be listed with the Secretary of State in your state (or the state in which the business is incorporated). Do you have a library card? Check your library's website. They may have a subcription to a service such as Newsbank which archives newspapers. I can go to my library's website and search our local paper back to the early 1990's. I can see when my kids were on the honor roll and read a letter to the editor of the paper which I wrote.
Another treasure trove of information is the local courthouse. Sometimes recent information is availabe on-line without substantial cost; however, often there is a steep set-up or monthly subscription cost. You can get around this by going to the courhouse in person. Since our firm subscribes to the records of several of the loca courhouses, I can go on-line and find out whether a person has sued or been sued during the covered periods. If they have, I can get copies of what was filed (which often gives my a person's medical history, in the case of accident victims). I can see if they own property, what it was worth when they bought it, what the tax assessor says it is worth today, and how big a mortgage was taken out. If someone had a bitter divorce, there may be interesting dirt in that file too. While you may not be able to access this information on-line, you can go to your local courhouse and find these records. If you need records from a non-local courthouse, you can request them, but the research and copying fees may be steep.
Almost everyone is covered by the Social Security system and when they die, you can find when and where in the Social Security Death Index.