Hm... well, the Wikipedia article is a bit difficult to read. I've been editing so far, but it's been clearly written by people who know a lot about the subject but don't know much about communicating it to the laymen.
Here's what you should try to do.
First thing's first, you should start off with something easy, written for the laymen.
http://www.hopkinsmedicine.org/press/2002/November/epigenetics.htm
That should do the trick.
Next you work upwards.
Go to
Entrez Pubmed
Click on the link, Books, near the very right of the black banner. Scroll down until you find Human Molecular Genetics 2. It's the Undergraduate textbook of choice. Look up Section 8, Human Gene Expression.
I can't remember off the top off my head, but I think Genome by TA Brown is pretty good too.
If you want a one stop site for finding out about Epigenetics, then I'm afraid you're out of luck.