I tend to run high in the character count because of the type of story I'm writing. The one I just finished has 4 main characters, and a total of 30 named characters. I often have four to five characters in each scene (five seems to be the max I can handle; six, and I start leaving one of the characters out).
The one thing I've learned is that isn't a number that defines too much--it's what you do with it. With my Civil War book, I dumped 11 named characters into the first chapter, and the comments I got back were along the lines of readers needing to write the names down to keep track of who was who. I ended up restructuring the beginning completely so that I only needed three, and then folded the others in gradually as needed.
I also do something with the character to make them memorable so that the next time the reader sees the character, they're likely to have not forgotten who the person is.
For large casts, it may also be helpful to keep a quick reference list of all the character names. I had one name that I had a lot of trouble spelling, and a list was very helpful.