Links for Further Research:
http://www.vladtheimpaler.com/vlad_the_impaler_bio_003.htm A site about Vlad in particular, seems to have a few historical sources.
A site about creepy things. Fairly corny, but useful for the tales about Vlad.
A site which gives the history of Vlad the Impaler in an unbiased way. It may have been translated from another language, as the wording is, at times, a bit off.