There are some really cute options, like these, and it would be really simple to make some pretty ones using fabric and washers. But, if you're looking for a quick and dirty (and free if you have a well-stocked pantry) solution I suggest tuna cans*. And Mexicorn**.
|Even handier since I cut knits on my kitchen counter!|
The piece shown in the picture above is the bodice for the dress I'm making myself. Here's a better picture of the fabric I'm using.
|I love the colors and it feels so nice|
As for the pattern--I'm attempting to make Simplicity 3503, the long view with short sleeves.
*Tuna cans are especially nice since they are low profile (aka short). You can put them near the pattern's edge and it's easier to get around them than a full-sized can.
**Mexicorn is taller than a tuna can, but a little heavier, so it's nice as well.