Backwoods Daydreamer has some good, inexpensive stakes that I like and use:
Also, your local Walmart or Academy Sports store may carry these, which are also very good and very cheap.
This type works most of the time for the kind of ground we have in this part of the country (mostly soft dirt/mud with occasional clay and some rocks in the soil).
Here's a good thread on rigging a tarp. My method matches the prusik method described most closely, but I use Nite Ize 9s instead of the knot.