My kids have always enjoyed brain puzzles, so I put together my own critical thinking curriculum for kids ages 3-6:
http://www.lalalogic.com . It has online "brain challenges" with games based on IQ test questions, as well as printable worksheets (with lots of cutting and pasting), and extension activities that include dramatic play, logic games, language development and other interaction that doesn't lend itself to an online format. It's only $25 per household one time fee for 100 "weeks" of content (that can be completed at your own pace, usually over 1-3 years).
I'd love to get some feedback from the members of this forum on the website / product if anyone wants to take a peek. I've been on the BK forum for a couple years now but not that active recently (trying to write computer software with three little kiddos around gets time consuming!). Thanks in advance!