Just a few ideas.....blowing on the clit, humming while you're at work....ice cubes can be interesting....different positions....edging.....denial (if she's into that)....also sensual play of the inner thighs.

I also know a lot of women plateau, which is normal physically & psychologically, but some women see this as a problem when it's not. So men need to also notice the signs of it & play into it on purpose.