In full disclosure, I feel that I should tell you to stop reading now, because the VistaPrint addiction spreads like crazy. That being said, I'd like to share a few things I use in my classroom:
Banners - totally awesome, and can be vertical or horizontal. (Usually you only pay shipping if you buy just one per order.)
Business Cards: so many uses! Usually, VistaPrint runs deals where you only pay shipping for a box of 250 cards, so it's not a huge investment...
Hopefully, you've found something you can use for your classroom!! If you don't already have a VistaPrint account, click here for a referral! If you already order stuff from VistaPrint, what's your "go-to" item?