Depends where you live. I am in the UK and use mothercare, boots and sainsbury alot :)
Mostly supermarket like tesco.
I've actually used consignment shops, yard sales, and Facebook groups for a ton of kine. Kept the cost down on a lot.
Craigslist, Goodwill, yard sales, consignment shops, and Target. Got most of my cloth diapers through Facebook groups like Cloth Diaper Swap.
Consignment stores and thrift stores are a life saver...no need to spend an arm and leg on something they'll grow out of in like a month..
Facebook groups and Wal-Mart .! (:
Wal-mart, Toys R Us / Babies R Us, Target