Claire if you were more specific it'd be easier to

. As Alice said leaving the onion out of a recipe is an option and there are a few veggies in the onion "family" such as scallions and shallots (and the leeks dandylin mentioned) that may serve the purpose, depending on what you're making and how you are using them.
I love onions and use them in most everything I cook...no ladies I don't bake desserts with them!
Check out this site, if nothing else, it's good for a

. rotflmao
http://www.antionionleague.cwc.net/