does anybody know the most famous american forums?websites that i can advertise on for my site.?

[Diamond]

[JPane]

Do NOT advertise your site on random American forums. That is spamming, which is frowned upon by the majority of the internet (except other spammers, perhaps). Since spammers are hated by most web users, you are not likely to convince them to visit your site if you become one.

From the Wikipedia article:

"Spam is the use of electronic messaging systems to send unsolicited bulk messages, especially advertising, indiscriminately. While the most widely recognized form of spam is e-mail spam, the term is applied to similar abuses in other media: instant messaging spam, Usenet newsgroup spam, Web search engine spam, spam in blogs, wiki spam, online classified ads spam, mobile phone messaging spam, Internet forum spam, junk fax transmissions, social networking spam, social spam, television advertising and file sharing spam."

https://en.wikipedia.org/wiki/Spam_(electronic)

You can form partnerships and affiliations with websites that have similar interests and purposes. For example, if you are an independent financial adviser, you should consider finding other financial advisers to advertise on their sites, in exchange for them doing the same.

You could also advertise through Google AdSense: http://en.wikipedia.org/wiki/AdSense

Finally, there are sites that allow you to advertise for free. Craigslist and eBay are two popular America sites that let you do this.

[WebDesign]

Go to google and type in your keywords and choose 'discussions' that will show you all the forums that will be related to your niche that are currently talking about it.

Join up and join in the conversation - be helpful not spammy. If you have your website link in your 'signature' often people will click on that to learn more about you and your product.