As someone who creates software for a living, I think it'd be insanely useful if users could list what ingredients they have available in their homes. So I could list a few things, like:

onions
green peppers
spinach
nutritional yeast
etc...

and the site would check the ingredients I've listed against the recipe database, providing me with a bunch of nicely sorted matches. From there, I can make anything that catches my eye with ingredients I already have in my fridge. :)

I would absolutely love this feature! It's actually something I was considering designing an app/site around myself, but you guys are already doing a good job.