The 2 most generally useful manifestos that I have read over at ChangeThis are:
Read them, absorb them, pass them around. The great thing about the portability of a manifesto is its absolute ease of sharing; it comes as a PDF so you can e-mail it and there are links within the manifesto to make the e-mail and sharing process even easier. There's no more trying to keep track of your book if you loan it to someone or having to purchase multiple copies of a book so that you can share it.
The 2 manifestos are in no particular order -- Seth's is a bit shorter -- and you should not necessarily read them in the order I have them above. What you should do is read both of them in a close period of time because they are extremely complimentary.
For those of you that have read all that Tom Peters has written, this is a great summation of topics that you will recognize; for those of you that are not at all familiar with Tom, this is a great introduction. For those of you familiar with Seth Godin, this, much like Free Prize Inside, is another big idea in business (not just marketing); for those not familiar with Seth, hopefully this will inspire you to become familiar with him.
It used to be that there was a cost of entry to access the knowledge of of Seth and Tom: the price of the books, the price of the seminars, etc. I am not saying that the books and seminars are not useful or worthwhile, but the cost of immediate entry just went to zero, and believe me, all of your competitors can afford that price.