The IDEA (International Dialects of English Archive) has a list of twelve different sound clips from speech instructors that give a varied understanding of the "standard" or "general" american dialect.
The General American accent can be found in many works. This CD in the Dialect & Spoken Word collection can help you understand how to recognize it.
This refers to the spectrum of ‘standard’ English spoken by newscasters, TV actors, and a large percentage of middle-class Americans.
Prominent Features:
Topher Grace and Rashida Jones are two great examples of the General American dialect, although many actors have what can be considered a neutral accent.