Your child's interest in toys will vary as their age varies, the key is to keep them challanged and entertained.
0-1 Years
Babies love soft, bright toys, espically ones that make noise or wiggle when they touch them. This is the perfect age for activity centers. At this age they won't be mobile for a while and babies love to bat at the toys and watch them wiggle round. They also love to look at themselves (or other babies, they can't yet tell the difference!) so anything with a mirror on it is sure to please. In my experience a sure smile winner is anything that makes music, because it almost ensures that the adult will start dancing along, and who doesn't love old people bopping to "E-I-E-I-O"
1-2 Years
This age group varies widly when it comes to surefire toys. I reccomend anything that can be adapted for play over the next year. They may not know how to put the puzzle together yet, or how to get the car down the track; but by watching you they will learn, and one day they will surprise you!
This is also a great time for ride-along toys, cars and bikes, they will love to scoot themselves all over the house. Tents, tunnels and puppets are also big hits at this age.
2-3 Years
By now your child will be able to name "Elmo toy" or "Dora ball" it seems like anything with a charater on it is a winner. Also at this age they can begin pretend play, kitchens, baby dolls and tool benches will help them pretend to be mommy or daddy. They are also old enought to actually use the Leapfrog systems and similar games to identify numbers and letters.