For Internet Explorer:
Add-on: IE Developer Toolbar - microsoft.com…
Application: VM’s for IE6, IE7, and IE8 – microsoft.com…
Application : Multiple IE’s – tredosoft.com…
For Firefox:
Add-on: FireBug – getfirebug.com
Add-on: Live HTTP Headers – mozilla.org…
Add-on: Web Developer – mozilla.org…
Add-on: YSlow – yahoo.com…
Add-on: Dust Me Selectors – sitepoint.com…
CSS Selectors
W3.org
Heather Solomon's Slide Deck on Branding Link Here
Real World Branding with SharePoint Server 2007 Publishing Sites http://msdn.microsoft.com/en-us/library/ee354191.aspx
Heather’s Base Master Page Files Base master page files with necessary content placeholders to run a SharePoint site. All branding and added code is stripped out.
CSS Reference Chart Informative chart of popular CSS classes and IDs.
A few more links on my blog: http://eschrader.com/2010/02/26/sharepoint-2007-branding-links/
MY SLIDE DECK IS ATTACHED AS WELL. http://spugs.org/LASPUG/Lists/Discussions/Attachments/2/SharePoint%20Branding%20-%20Single%20SharePoint%20Sites.pptx
If you have any questions, just ask :)