Everyone's tastes will be a little different, so I hesitate to make name suggestions, but perhaps answering some questions can help steer you in the right direction.
Since you had some girls' names picked out, could you "masculinize" those?
What about your husband's, father's or father-in-law's name? Or the name of a family friend or other family member? My oldest son has my father's middle name and my FIL's first name; my younger son's middle names is the same as my husband's.
What about Bible names? While many are common, some are not--and almost all of them can easily be spelled. That was one of my requirements--that my kids wouldn't have to always be spelling their names. You may not feel that way. You may also have a favorite name from a book or TV show.
What about making your name, or the name of some female in your family or among your friends masculine? "D." can become "Daniel."
There are many websites where you can look up names by their meanings, so if you have something in mind for a good meaning, you can go from there. (For instance, "Matthew" means "Gift of God.") You could combine this and another technique, by finding out what are the meanings of names (such as your husband's) and then seeing what other names have the same or similar meaning.
You could perhaps limit your search to a certain letter or a few letters. For instance, you could have your son's initials be the same as your daughter's, or your father's or grandfather's.
You could also on some websites pick how the name ends--for instance, -el names could be Daniel, Nathaniel, Samuel, etc.
If you want to make sure your son won't be one of five kids with the same name in school, I'd suggest looking at "top baby names" lists and eliminating all of the most popular ones.
Good luck!