Most people are drawn to patterns. Hence, we coordinate things. We create sets of things that that match, or that have some element in common.
This logic is often applied to baby names. Many parents-to-be will wonder, for example, "Does this name go with the names of my first two sons?" Or, "Will this name limit me in terms of what I can name my next child?" They don't want their children's names to be totally mismatched ("Here are my kids: Gudmund, Maritza, Siddhartha and Yong"), which is quite understandable.
One of the most common ways to tie sibling sets together is by sound. Actor Vince Vaughan has siblings Valerie and Victoria; many of the twins born in the U.S. have distinctly similar names as well (Ella & Emma; Isaac & Isaiah; Landon & Logan). Taken to an extreme, however, this type of matching can turn into a bad thing. Names that are very alike, or that rhyme ("Huey, Dewey and Louie") can not only cause confusion on a daily basis, but also potentially affect the children in a negative way (i.e., the kids will resent not having individual identities).
What are a few of the less obvious ways to match sibling names?
You could match names by origin -- choosing names with only Germanic roots, for instance, or choosing only French names. This would be a great option if you are particularly proud of your heritage.
You could also match by historical period -- going for names that were popular during the Victorian age, for example, or that were big during the Roaring Twenties.
Finally, you could match by association -- picking names out of your favorite book or movie, or picking the names of scientists you admire, or sports stars you look up to.
These aren't the only options, of course. If you have a few other ideas, please feel free to visit the BellaOnline Baby Names forum and share them!