I really like this set from LEGO. The DUPLO line is intended for children 18 months to 5 years old, but I think older kids will enjoy it as well when they combine pieces to make more complex designs.
The #1 reason I like this set is that the great majority of the pieces are easy to hold, easy to assemble, and hard to swallow. I encourage families to remove the smaller pieces until their child is not prone to putting small things in their mouth. But that still leaves so many pieces left for fun!
Young children struggle with asymmetrically-shaped pieces, so simple squares and rectangles are easier to manage. The larger squares with numbers on them are especially easy to hold; they fit securely into the palm of a toddler and provide surface area for them to place their fingers securely on the sides of the blocks as they put two together.
In addition, the colors and the numbers are great for early learning. Some of the families I work with get two sets and work on matching numbers and colors while they are working on grasp and coordination.
Oh, and the set is under $20 U.S. Nothing like a value to make me smile!!!