It is important that beginning counters learn 1-to-1 correspondence. Correspondence is the understanding that a number symbol stands for a group of objects. For instance, the #3 is used to symbolize 3 buttons. In this example the buttons are the "unit." Have fun experiementing with many different units to teach this concept.
Unit: Circle Punches A Listmaker's Life demonstrates an activity matching foam letters to cardboard punch outs.
Unit: Clothes Pin This fun idea from Blissful Moments allows you child to clip a clothes pin to each sticker on small paper plates. They can count as they put them on and as they take them off.
Unit: Stickers Ten Kids and a Dog shares a simple idea for using reinforcement tab stickers to practice counting.
The Adventures of Bear submitted a similar counting activity using stickers. Notice that she has provided scaffolding to help her young learn. (Meaning: the dots are available to put the stickers on)
Amy at Teach Mama has a great idea for getting your kiddos outside in the sunshine and using mother nature for some learning fun! Check out her Backyard Number Boxes.
For more information about teaching basic counting skills read Tracey's post at Girls to Grow: Beginning Math Skills.