What I've had fun with:
Rose Art Scented Glitter Gel Pens: these have the same sort of barrel as an RSVP pen (except there is glitter in the plastic!), so I stamp a piece of paper to match the color, unscrew the end, roll up the paper and insert it in the barrel. I include these in door prizes and hostess gifts. I found them at Dollar Tree for 3 for $1.
Translucent colored plastic note pads: These have a clear colored cover with a white paper behind it, making it fun to stamp the front with a design in Stazon, then stamp on the paper behind with Little Shapes or something else. Particularly cute done with Little Layers. They come three to a package for $1 at the Dollar Tree. Haven't been able to find them lately, though
Inexpensive Pillar candles for $1. These make nice candles for doing tissue paper on candle stamping or for wrapping with stamped cardstock and can be given as hostess gifts or used for stamp camps. Just be sure to warn them that they should not leave them burning unsupervised, or should only burn them down far enough to insert a metal-encased votive light...then they can keep the pretty part nice for ever with out burning it down.
Metallic or Pearl painted pencils. Ink up the Filligree background stamp with Stazon and roll the pencil across the stamp to create stamped pencils! Very pretty. I include these in door prizes or hostess gifts. You can get 10 or 12 for $1 at the Dollar Tree.
Spiral bound index card books. I found these ONCE and have been looking for them ever since. You can make a cute cover for recipes, in fact every time I show one of these in my display, someone offers to buy it. I found them 2 for $1. They make great hostess gifts or door prizes.
Vinyl covered date books (checkbook style): Dollar Tree has these before Christmas. They are a little better quality than the Michael's ones (which are clearanced off right now for 33 cents! a better deal, though they aren't as nice). I stamp a cover to insert over the one that comes on the calendar. If there are pictures on the inside of the calendar, I try to match to a stamp set. These also make great hostess gifts or door prizes, but you need to use them up quickly, since no one will want one after the end of March.
One thing to keep in mind is that if you see something you like at a dollar store, buy one to experiment, but if you are successful and you want more go immediately and buy as much as you can. They don't always stock the same items and when they are gone, you can't depend on getting more.