Some SEO's do not agree that Google uses some special filters to rank a site but many SEO's believe in these filters and also give evidence on the existence of these filters.
The reason behind these filters is still unclear, but most probably they are applied to stop spammy sites and the sites using unethical SEO to get higher positions in Google search engine. These filters are either built in Google Algo or applied time to time individually in case of Google Bomb (simply awesome )
Here is a list of known Google Filters and their description.
Google Sand Box Filter
This Filter basically placed on new websites. Due to this filter a new website does not receive high ranking for its major keywords. Sites that are using high competetive keywords affects more by this filter. The reason for this filter is to discourage the spam sites to use spammy techniques to get 1000 links a night for high ranking.
A website can stays in Sand box for one to six months. TO get put from sand box you have to wait and wait.During this time add content to your site and get some quality links.
Google -30 Filter
To get out of this filter immediately remove all spams methods you are using on site and offsite. This filter seems to be automated so after some time of removing spammy things you will see your site again on good ranking.
Google Duplicate Content Filter
This filter is applied to those sites having duplicate or same content. This filter results a drop in your sites index pages or even complete removal of your site except your homepage.
Problem is that If your site is much newer than some other sites who has domain age of two years and they steal your content than You have to suffer from this filter. Its sad but its true.
To get out of this filter use unique meta tags for each page and avoid use of duplicate content.
Google Domain Age Filter
This filter was set up to give older domains more credibility than the newer ones. If your site is there for longer time duration than your site gets more attention by google.
Google Trust Rank Filter
This filter decide the trust rank for a website, which is determined by the age of domain, quality of inbound links and content of a website.
To increase trust rank of your website get quality backlinks and use natural content.
links.htm Page Filter
This filter apply to pages labeled with LINKS. Many sites has a page for link exchange and mostly they use LINKS in url and title for that page.
To avoid this filter use something else than LINKS for your link exchange page.
Google Omitted Results Filter
This filter applies to the pages Google think may have duplicate content. So instead of showing all these pages, it choose one or two pages from that source and give an option in the end to include omitted results. Google offers the Omitted Results link in shortened queries.
To avoid this filter use CSS to show the unique content first to search engine crawler.
Link Farming Filter
Pages with nothing but list of Links and Links and.. OK .. enough. These pages are created to get more links pointing to a website, but Google now apply a filter on such pages.
Don't participate or place your link on any pages which seems to be a Link Farm.
CO-citation Linking Filter
This filter apply due to your website Outbound Link Structure. If your site has a link on a website that links to automotive sites then according to Google your site will also be relate to automotive.
To avoid such type of Filter Think Before You Link!
Too Many Pages At Once Filter
This filter applied to website have too many pages in a very short period of time. To avoid this filter don't use content generator softwares or stop copying other sites content.
Too Many Links At Once Filter
This filter applies to the site that gets too many links in very short span of time. To avoid this filter don't participate in Link Farms or Any Spammy Get Link Campaign.
Over Optimization Filter
This filter applies to the site using more than required optimization tips. For example stuffing keywords and use them un-naturally or using title tag as keword tag.
To avoid use of this filter be gentle and patient.
Broken Link filter
This filter applies to site having link to pages that doesn't exist whether it is external page or internal page.. Since Google gives special attention to links so this filter badly affect your site ranks.
To avoid this filter don't link to pages that are no longer exist on web.
Google Two Word Keyword Filter
Using two main keywords excessively trigger this filter.
Don't Use same two words in your url, acnhored links
The Network Filter
This filter applies to the network of sites having each other links on their sites. For example you have 5 websites and they all link to each other.
The Hyphen Filter
Having hyphens in your domain name may trigger this filter.
Slow Load Filter
If your site takes too much time to load then spiders dint crawl your site and your pages will be removed from index.
If you are searching in Google than the sites you get on top ranks are most likely hosted in same country as you are in.
Google Porn Filter
Google is in safe search mode by default. And it wil exclude the sites which it suspect tto be adult sites.
Google Bomb filter
The Google bomb filter seems to be applied to web sites that get too many identical links in a short time period
Alleged Dampening Filter
This filter applies to the incoming links. If you got a link than its not immediately start passing Link Juice but Google apply a dampening filter on that link result in a partial immediate credit.
Here are two good sources from where you can find more info about Google Filters.
If you know anymore filters or penalties please suggest them.