Perfect Rhymes (not common words):
* ditch (not usually used in the same context)
* twitch (can be used metaphorically, like "the light switch gave a twitch")
Near Rhymes:
* hitch (meaning to fasten or connect)
* stitch (can be used metaphorically, like "a stitch in time saves nine, so fix that light switch")
Eye Rhymes:
* rich (doesn't sound like "light switch" at all)
* which (doesn't sound like "light switch" at all)
Creative Options:
* Phrases: "turn it on" or "flick the switch" could be used in a poem or song.
Ultimately, the best rhyme will depend on the context of your writing.