there are many md5 library/ crackers now that you just add the hash and it will find wheat the word is. This generally only works with dictionary words.
I don't know what type of site you're seeking encryption for, but if you're merely trying to avoid storing raw passwords on your average site, using a standard method (such as md5 or sha1) along with salting it with an unknown and random (yet static) string should be more than sufficient. There are obviously numerous stronger methods than I mentioned, but they are also less efficient and thus unless needed, wouldn't exactly be practical.