I HATE chopping onions every time I need them for a recipe. Also, onions are usually cheaper in bulk so if you buy a bag and don't use them right away, you usually have a few go rotten. Fortunately I've realized that onions freeze very well.
I recently started chopping my entire bag of onions and freezing them in small quantities. I like my onions practically pureed for most recipes so I put them in my food processor and put varying amounts in those cheap fold over bags. Then I stuff all those fold over bags into a bigger ziplock bag. You can chop them into whatever size(s) you think you will need and then whenever you need onions for a recipe you just pull the baggie out and thaw it under running water in a strainer. Believe me, this will save you tons of TIME and TEARS. Try it out the next time you buy a bag of onions.