favorite building toys for 4 and 6 year olds?

[skohng]

I need an affordable building toy that will entertain my 4 and 6 year old boys. We have magnatiles and legos of course, and I know there's the M&D building blocks. Anything else? No kinex or anything similar; just basic shapes that stack and interlock for quick building. Thanks!

[Melaine]

My girls love citiblocs. http://www.citiblocs.com/

They have some nice unit blocks, some alphabet blocks and lincoln logs but I think the citblocs are the coolest and get the most play.

[swissair81]

Bristle blocks?

[hellokitty]

Trio
Citiblocks
Marble runs
Kids knex (they have knex at mil's house, but haven't used them much yet)
Lego

[hillview]

Duplos
Unit blocks

[kristac]

My 4 and 6 year old love this set of blocks- I recommend 2 sets
http://www.bedbathandbeyond.com/product.asp?sku=18453738&utm_source=google&utm_medium=organic&utm_campaign=shopping