Black Hat SEO – Hidden Content
There are many ways to hide content on your site. All of them are black hat SEO methods.
Another black hat SEO method is using comment tags to hide keywords. For example:
<!–hidden content, hidden content is bad, hidden content in comment tags is bad–!>

White Hat SEO – Quality Content
Content that targets a strong, related keyword phrase on each page wins every time. After you’ve chosen your keyword phrase, use it consistently throughout the page.

• Linking

Black Hat SEO – Link Farming
The idea behind link farming is that you exchange links with other websites to boost your site’s rank in search results. Search engines like Google examine how many sites are linking to yours when determining rank.

White Hat SEO – Inbound Linking
When someone links to your blog post or a page on your site within their content, you have a quality inbound link. Unlike with black hat link farming, inbound linking is not a link list traded for the sake of boosting your search results.

• Page Elements

Black Hat SEO – Doorway Pages
Doorway pages are known by many names, such as bridge pages, entry pages, gateway pages, jump pages and portal pages. These pages are created to spam search engines with a certain phrase.

A doorway page is created to get traffic based on keyword phrases and then funnel those site visitors to the main site. Most search engines catch doorway pages and sites are penalized.

White Hat SEO – Headings
A better use of page elements is to break up your page visually with SEO-friendly headings. An article using <H1>, <H2> and <H3> tags that make good use of your keywords has more weight in search engines than a page full of regular-sized text.
References :

breaks search engine rules and regulations
creates a poor user experience directly because of the black hat SEO techniques utilized on the Web site
unethically presents content in a different visual or non-visual way to search engine spiders and search engine users.

White Hat SEO
Any SEO tactic that maintains the integrity of your website and the SERPs (search engine results pages) is considered a "white-hat" search engine optimization tactic. These are the only tactics that we will use whenever applicable and which enhance rather than detract from your website and from the rankings.

You can check here to know about Black Hat / White Hat SEO
http://www.ahfx.net/weblog/55
http://advertising.about.com/od/onlineadvertising/a/whitehatvsblackhatseo.htm
http://www.beanstalk-inc.com/tactics/white-hat.htm
http://websearch.about.com/od/seononos/a/spamseo.htm
http://www.whitehatseo.com/
References :
http://advertising.about.com/od/onlineadvertising/a/whitehatvsblackhatseo.htm
http://www.ahfx.net/weblog/55
http://www.whitehatseo.com/
http://websearch.about.com/od/seononos/a/spamseo.htm
http://www.beanstalk-inc.com/tactics/white-hat.htm