My toddler goes nuts for scissors and glue and anything she dubs "arts and crafts" so I'm always on the lookout for stuff that fits the bill.
Mr Printables fits the bill! It's got a ton of cool paper crafty stuff for kids, and the cone girls have been a big hit around here.
And PaperMatrix has some beautifully intricate paper crafts for those of you up for a challenge. I want to try my hand at those hot air balloons someday.
(Thanks to How About Orange for the tips.)