As far as household stuff there are two things that make me happy every time I use them:
1) a GOOD set of knifes (even just 2, a chef's and a paring). Something nice that can be resharpened, hold an edge, and get really sharp. Personally I have Wustoff (and get a new one every Christmas from my wonderful step-mom )

2) Salt and Pepper grinders. I can't believe how much better things taste with fresh salt and pepper, and if you can get them in bulk it's no more expensive than the pre-ground stuff.

If you aren't a microwave person, yes, a toaster oven would be a good investment for heating up leftovers (you'll have a lot of them as a single person if you cook. I cook 2-3 times a week and eat leftovers pretty much the rest of the time).

Other than that (and slightly, but not totally, irrelevant) my dog! Seriously, can't live without her, for many reasons. Not the least of which is that she makes me less edgy when I'm alone (I jump at every little noise at night when I'm alone, but not so much with her around).