Dehumidifiers and humidifiers hooked up to a controller that has a meter that reads the humidity of the room. Quest is a really good company but kind of expensive.
AC is usually my favorite way to handle it because in small grows it deals with heat and humidity at the same time. If the AC can't handle the humidity, a quality dehumidifier will. If those options are too expensive, getting more powerful fans to increase the rate of air exchange is probably the best alternative.
A really cheap and easy way to lower humidity for microgrows is just throwing some small food desiccant sachets in the container, or just anywhere near the soil. It has worked really well for me. The humidity rarely stays above 60 for more than 24 hours after watering.
Ya well, I have a couple of reasons for not going that way.
First and foremost, more air movement means a bigger fan and that will be noisier, mine is a stealth grow and no noise is a must.
Second, the air here is pretty humid, so I would rather have a solution that ensures the air is dry inside the box, giving me the tranquility that I won't have bud rot.
Last, but not least, I'm kind of a perfectionist regarding the ambient inside the grow box (humidity, temperature, night temperature drop and air exchange) all this has allowed me to have fast developing plants with very tight node spacing. So I would rather keep the air exchange in it's current rate.