Though play comes naturally to most 3-year-olds, preschoolers still need help finding safe and developmentally appropriate toys. Try to resist the temptation to rush out and buy the latest "educational" toys on the market or whatever's hot on TV. A good set of blocks that can be played with in many different ways is more likely to teach math skills than is an expensive electronic toy that works only when you push certain buttons.
Also, try to avoid sexism. It's perfectly okay for preschool boys to play with kitchen toys and for girls to play with trucks. Such choices do not determine sexual orientation. However, depriving a child of certain toys or experiences on the basis of gender does short-circuit creativity and growth. The other extreme -- forcing dolls on boys or footballs on girls -- can be harmful, too. Studies show that even in the most gender-neutral environments, boys and girls tend to play with different kinds of toys. Your best bet is to follow your child's lead.
Another rule of thumb: Less is more. Although an expensive, store-bought dalmatian costume would probably look adorable, your child will have just as much fun-and use more brainpower-pretending to be a puppy with cardboard ears and a pin-on tail. Some of the best play materials for this age group are items that cost nothing: a wrapping-paper cylinder to use as a telescope, an old pair of boots for exploring in, an oversize box that can serve as a car. Open-ended items that invite hands-on experimentation give your child the freedom to pretend and learn -without inhibiting rules and constraints. So consider recycling household items as toys.