Mini business cards! I love anything miniature and these are just so sweet. They're from Moo, a printing company I came across from a blog I just started reading, megan E sass. If you have an Etsy shop, you can take advantage of an offer they have going to get 100 of these little cards for free (though there's a $5 shipping/handling fee). If you ask me, $5 is totally worth it for these high quality, front and back printed cards.
I'll give you a look at a couple other cheap things I've taken advantage of to get the word out there. In the past, I've ordered business cards from Vistaprint, which I purchased a deal on (I can't remember if it was Groupon or LivingSocial), so if you're looking to get a deal on business cards, keep an eye on the deal sites. At the time, I didn't know what I really wanted to specialize in, so I designed some generic ones in Illustrator with my logo and info that were pretty versatile.
There are lots of websites now that show DIY business cards. For the sales I make in my shop, I don't like using my fancy cards to attach to packages, so I often make quick tags with my website info on there and tie them on the item with some matching bakers twine.
For these, I use scrapbook paper I've had around forever cut into 2"x4" rectangles, a corner punch, a slot punch for the hole (or just a regular hole punch), and a stamp kit I found at a garage sale. The kit is one of the best things I've found at a sale and it can be used on a lot of different projects. It's similar to this one that I found at a flea market. Both were under $5 each:
I also designed a stamp and had it made into a self inking stamp on Vistaprint using that deal. I use it to stamp random things, like the outside of packages.
So there you go! A few ideas that I use to promote my shop. Have a great weekend!