The biggest scores have come from the huge consignment sales that happen around my area every spring and fall. Most cities have mom groups, and those mom groups have sales. The sales usually start at 8:00, but if you're looking for something big then you need to get there early - people start lining up an hour before the doors open and then it's a mad dash to where the big ticket items are located - the strollers, high chairs, jumperoos, big toys, and furniture. Last year I was after toys - I came away with a push toy and a ride-on toy for $5 each, both in great working condition. This year I was only after clothes. Charlie needed a spring/summer wardrobe.
What did I end up with? This lovely collection.

Four pairs of shorts (1 Jumping Bean, 1 The Gap - new with tags, 2 Old Navy), two pairs of cargo pants (1 Cherokee - new with tags, 1 Old Navy), a bathing suit (Old Navy - new with tags), and a UV protection shirt (Old Navy). None of the used clothes had any stains or tears or marks that indicated that they had been worn before. How much did I pay for all of this? $13.
That's pretty good for a stash of shorts that should last him the whole spring and summer. I might need another pair or two, but there's a calendar full of consignment sales running through the next month.
My extra bonus was this wooden Tonka Truck - it didn't come with the box, but it's in perfect condition. I bought it for $1, and it's going in Charlie's pagan fertility ritual easter basket.