Adding SharePoint Lists and Libraries using SharePoint Designer
http://office.microsoft.com/en-us/sharepointdesigner/HA101487201033.aspx
http://office.microsoft.com/en-us/sharepointdesigner/HA101174371033.aspx

SharePoint Designer Workflows
http://office.microsoft.com/en-us/sharepointdesigner/CH100667661033.aspx

HTML Code
http://www.htmlcodetutorial.com/
http://www.web-source.net/html_codes_chart.htm

CSS
http://www.w3schools.com/css/
http://www.w3.org/Style/CSS/

Master Pages
http://office.microsoft.com/en-us/sharepointdesigner/CH100667701033.aspx
http://www.heathersolomon.com/blog/articles/BaseMasterPages.aspx

Master Page Templates
http://office.microsoft.com/en-us/help/HA102223711033.aspx

SharePoint Branding
http://www.cleverworkarounds.com/

Core CSS Customisation
http://www.heathersolomon.com/content/sp07cssreference.htm

Publishing Pages in SharePoint
http://office.microsoft.com/en-us/sharepointdesigner/HA101741331033.aspx

Books on SharePoint Designer

Microsoft Office SharePoint Designer 2007 Step by Step – Penelope Coventry Microsoft Press Professional

Microsoft Office SharePoint Designer 2007 – Woodrow W. Windischman, Bryan Phillips, Asif Rehmani Wrox

Building Web Applications with Microsoft Office SharePoint Designer 2007 Step by Step –
John Jarsen Microsoft Press

Microsoft Office SharePoint Designer 2007 Bible – Vikram Kartek Wiley