I've found that working within a theme helps organize the whole party. If you are doing a Thomas the Train theme, you can do games around trains, decorate room like a train station, and give out goodies associated. If you are doing a fiesta, you can do pinata, water balloon relay race, egg on spoon relay race, pin-the-tail on the donkey, a craft. All types of things that don't take a lot of time, money or energy. Three year olds are happy with a craft, a few games, a puppet storytime or regular storytime, pizza and cake. Some people even opt not to have toddlers open gifts in front of guests, as they are still learning gift-giving etiquette, but will have child give goodie bags out as guests leave. Do not give out goodie bags while guests are still staying, as the children start asking for more goodies or someone else's goody. My favorite parties, though, are at party places, like Chuck E Cheese or My Gym where the staff does all entertainment and you just bring a cake and juice. Usually $50 more than at home, but so worth the extra without cleanup and prep time. Plus, the kids [and adults] have an absolute BALL!