Michael's post of yesterday had some great advice about naming characters (! and your children !). But what if you're fishing around in the past and need some realistic names for characters from "back when?" I doubt there were very many women named "Tiffany" or men named "North." But, my feeling is as long as you have someone exclaim, "How'd you come by THAT handle?" (or some such), you can get away with a lot (unless you try for, oh, "Laser" or "Quasar" in 1600s, for instance).
I'm lucky in that I have several venues open to me to suss out what might be reasonable character names for my time frame and location of fictional choice (U.S. West in 1880s). There's the lovely Social Security "Top names of the [pick your decade]" website at http://www.ssa.gov/OACT/babynames/decades/. The thing to keep in mind is that these are BABY names. Alas, the earliest decade is 1880s, but I think one would be pretty safe in picking names from this group to project back a few decades. Here's a little screen shot of the "Top 10 Faves" for babies born in the 1880s:
I love that Minnie, Ida, Bertha, Clara, and Alice show up here as popular. They are somewhat unusual names in current days and times, so I would think if I have a woman character I would want the reader to remember, giving her the name "Ida" might help.
Here's another cool place to view names... and these tie to year of birth, so are even more useful: http://www.galbithink.org/names/us200.htm. So, suppose I have a woman character who is 30 years old in 1880. I can go to the 1880 census in this list, and view names that appeared for women born between 1841-1850, right here. Sure, there are PLENTY of Marys (3557 out of a sample size of 22665), but there are also names such as Easter, Sophrona, Almira, Mahala, Lee ... and even Rhonda (which I think of as a more "modern" name, but there you go!).
Other places to look for names include newspapers and various genealogical collections. For instance, I happen to be distantly (VERY distantly) related to the du Ponts (yes, as in chemicals et al). In 1951, Pierre S. du Pont printed up a mammoth genealogy stretching from 1690 to 1951, and then provided copies of the gi-normous binder to all the descendants (well, that's the story anyway). I can wander through this "gift from the past" and uncover given names from the mid-1800s such as Lammot, Eleuthera, Alletta, Emilie Ann (who, according to footnote, was known as "Mimi"), Nevil... as well as plenty of Williams, Thomases, Marys, Roberts, Janes, Johns, as well as, Claras, Idas, and Alices.
Who's to say there might not be a Tiffany among them, somewhere?