A lot of the time, when I come up with an idea for a novel, the characters are nameless. I can see them, I just don't know what to call them yet.
Sometimes, names for characters just come to me. Robin Bailey, for example. Not really sure how I came up with it. I just...did. Seems like a good name for a brave girl like her, doesn't it? And the first and last name seem to really go together. I actually think I made up most of the names for that series on the spot. There are a few exceptions. When I created Bartholomew, I wasn't sure about his name right away. But since Nathaniel is a Hebrew name, I thought Dr. Rollins's brother should also have a Hebrew name. And they both sound so elegant and sophisticated, which is how they try to come off. Also, I had a hard time deciding on Riley's last name. Riley, of course, is an Irish name, so I browsed a long list of Irish surnames before I settled on Jenkins. Again, it just sounds right!
If you're stuck and looking for inspiration, I like to look at baby names web sites. My favourite is babynames.com. You can browse names by gender, origin, number of letters, and what the name starts with. So if you have a character with French ancestry, look up some French names. If you want a three-letter guy's name, you can do that, too. I've been using this a lot for my works-in-progress. It's also neat because you can see the meanings of the names, so maybe you'd like to choose a name whose meaning relates to your character's personality.
Finally, maybe you need a name that sounds like another name. For example, for my NaNoWriMo 2012 novel, I'm making a modern retelling of a rather famous story. [Hint: My NaNo novel is called Phantom Desires.] So, I tried to choose names that are similar to the existing characters's names. Again, this is where baby names web sites come in handy! I used the "starts with" feature. My protagonist's name just had to start with a C, and one of her love interests had to start with an R (more hints . . . please tell me you're catching on!), so I entered that info into the search and voilà!
If you need surnames, just Google surnames of the origin you want, like I did for Riley Jenkins. Those are harder to think of, for sure. I think it helps if you already have a first name. Then you can test out how the first and last names sound together.
I hope this helps you! Or, maybe you have your own strategies for naming your characters. If so, I'd love to hear about them in the comments. I could use the help!