http://msdn.microsoft.com/en-us/library/aa543341.aspx

Lots of posts saying how to customize it, but it shouldn't be done,

Use custom content types instead and point them to a nice custom ASP.NET page instead

http://www.sharepointkings.com/2008/05/how-to-edit-list-forms-like-newformaspx.html
http://sharepoint07.wordpress.com/2008/02/05/customize-the-newformaspx/
http://blah.winsmarts.com/2007-5-Customize_the_-and-quot;NewFormaspx-and-quot;_page_for_a_SharePoint_List.aspx
http://vspug.com/dwise/2007/11/14/lesson-learned-while-customizing-newform-aspx/
http://www.risetime.com/blog/archive/2009/06/03/create-a-custom-newform-aspx-for-a-sharepoint-list.aspx
http://blogs.msdn.com/scaravajal/archive/2007/04/29/sharepoint-designer-and-newform-aspx.aspx

http://weblogs.asp.net/jan/archive/2006/11/06/Custom-Edit-Forms-for-SharePoint-2007-Lists.aspx

http://weblogs.asp.net/gunnarpeipman/archive/2009/06/05/sharepoint-customizing-dispform-aspx-and-editform-aspx-through-browser.aspx

http://nishantrana.wordpress.com/2009/01/30/read-only-field-in-sharepoint-editformaspx/

http://sharepointsolutions.com/sharepoint-help/blog/index.php/2009/10/using-enterprise-content-types-and-managed-taxonomies-in-sharepoint-2010/

http://sharepointmetadataandclassification.typepad.com/blog/windows-server-fci/

http://blogs.techrepublic.com.com/networking/?p=1622

http://blogs.techrepublic.com.com/networking/?p=1441

http://www.tonstegeman.com/Blog/Lists/Posts/Post.aspx?List=70640fe5%2D28d9%2D464f%2Db1c9%2D91e07c8f7e47&ID=56
http://www.mindbusiness.de/blog/2007/05/02/sharepoint-folders-and-metadata/
http://kartickapur.wordpress.com/2007/10/26/folder-content-type-and-associating-views-specific-to-that-folder/
http://amatterofdegree.typepad.com/a_matter_of_degree/2007/05/moss_2007_bug_i.html
http://www.dotnetmafia.com/blogs/dotnettipoftheday/archive/2008/01/14/creating-a-content-type-based-folder-in-sharepoint-via-feature-receiver.aspx
http://blogs.msdn.com/ketaanhs/archive/2008/02/09/how-to-attach-attributes-or-metadata-to-folder-in-sharepoint-2007-moss-document-library-or-any-sp-list.aspx

http://grounding.co.za/blogs/brett/archive/2008/09/09/sharepoint-content-type-id-s.aspx

http://mdablog.spaces.live.com/blog/cns!B0C40902E1212960!382.entry

(via What Are Content Types, Anyway-)

Nice explanation of Content Types in Sharepoint

http://johnholliday.net/archive/2006/10/20/Content-Types--The-Soul-of-a-New-Paradigm.aspx