United States Patent and Trademark Office has many useful links on trademarks including:
United States Trademarks: links to Trademark Electronic Search System (TESS) and more
Background information about trademarks
USPTO Forms provides many forms.
Trademark Electronic Application System (TEAS) allows official filing on-line.
Intellectual Propery Resouces guide from the Los Angeles Public Library Science/Technology/Patents Department offers information on trademark searching using Cassis, a CD-ROM product of the U. S. Patent and Trademark Office and help on how to conduct a trademark search. Staff is not permitted to perform searches, fill out forms, or give opinions or advice.