To clean your sink disposal: Throw in some ice cubes and lemon halves. Switch it on, turn on the water, and let it run until it sounds like it's done.
When boiling eggs: Add 1/2 teaspoon of baking soda to the water. The shells will slide right off when they are done cooking.
Leftover quinoa: Makes a star addition to a breakfast bowl. It's a superfood, high-quality protein, and I don't know about you, but when I make it for dinner I end up with tons of it leftover. I pile it up on top of Greek yogurt with some blueberries, almonds, and ground flaxseed.
Salad bank: I have an enormous popcorn bowl with an airtight lid that I use for salad greens. Each week, I buy a large tub of prewashed greens and dump it into the bowl. If you keep the lid on it, the greens will keep for awhile and I can just reach in and grab a handful for a quick salad in a pinch.
Fruit/veggie wash: I fill half my kitchen sink with water and throw in a cup of plain white vinegar when I get home from grocery shopping. Then I dump all my produce in (sometimes in batches if I have a lot) and let it all float around for about 10 minutes before putting it away. All the gunk stays in the water and I can rinse it, dry it, and it's ready to eat. This helps them last longer in storage too and I peel off the little stickers as I put them in the sink so I don't have to worry about that later.
Caring for non-stick cookware: One of the sales staff at Williams Sonoma told us to never, ever use spray-on cooking oil in our non-stick cookware. It will damage the teflon and make it flake off into your food. She also told us to never heat non-stick beyond medium heat, as that will damage it as well. Wait until it cools before cleaning it.
Cooking crab legs: I pounce on crabs legs when they go on sale. To cook them, I wrap themin clean dishtowels that are damp, then seal them up in plastic wrap or a large plastic bag. I pop them in the microwave and cook on full power for two minutes. Perfect crab legs every time.
Microwave popcorn: Expensive and bad for you to boot. I buy bulk popcorn and pop it in a paper bag in my microwave. Just pour about 1/3 cup of popcorn into a plain paper bag, fold down the top a couple times, and pop it on full power for about 1.5 minutes. No nasty chemicals. You can add a little melted butter, salt, whatever you want.
I have more, but that's what I can think of off the top of my head.
(Edited for typos)