Be sure to match whatever dimmer you buy to the technology used by your lights.
Look specifically for Incandescent/halogen, CFL/compact fluorescent, LED, whatever type your lights are.
a nice add on to this would be those lovely timer controllers for bathroom fans (usually 3-6 settings between 10m, and 60m), say a 3 pack of them for people who are sick of turning off fans for people… 
I don’t need no stinkin’ biscuit, I need white!
You’d be surprised… I tried installing 2 LED dimmer switches on a set of lights for a chandelier. Neither of them worked, I think because the wattage was too low. When I installed 4 LEDs with a normal incadescent (56 watts total), it worked as expected. I ended up buying a conventional dimmer switch with a toggle. It turns on (more than the LED dimmer switches did) and allows you to dim, although we hardly use this function. The lower level is lost, but it doesn’t flicker light the original dimmer switch did, which is an improvement.
A few years ago, there was a lot more differentiation between dimming for incandescent/halogen and dimming for CFL/LED. You could get a dimmer for just dimmable LEDs and it wouldn’t work for incandescent bulbs (which was SUPER annoying as an electrician). These days, it’s pretty hard to get a dimmer that works for LEDs that doesn’t ALSO work with incandescents/halogen/CFLs. However, you can still definitely get dimmers that only work with incandescent/halogen bulbs. Always need to look on the box. Plus, there’s often symbols on the dimmer itself that will denote support for CFLs and LEDs, you just have to look for them.
That said, after a little research, the dimmers offered here are only for incandescent and halogen bulbs. If you have CFLs or LEDs, don’t buy these.