I have a text that I would like to have recorded by a professional. 
The product is likely to be sold commercially, so a real voice pro is
needed.  Ideally, will have his/her own recording equipment. 
Compensation negotiable based on experience.

Dear Tony, 

There are several agencies specialising in voice artists, which can
provide you with suitable aritsts, including meeting specifications as
to gender, accent, etc. Most artists can send a digital file through
the Internet. That means, that even if you're located in the US and
would like to have an announcer with a British accent (or who usually
resides in another area in the US, this is possible).

Here are several such leading agencies: 

Voice123
<http://voice123.com/s/voice_over_artists.html> is a voice-over
marketplace, where you can post a job for voice artists and get them
to answer you.

Commercial Voices
<http://www.commercialvoices.com/> - a voice-talent agency

Lip Service
<http://www.lipservice.co.uk/> 

Another Tongue
<http://www.anothertongue.com/katana/> 

Excellent Voice
<http://www.excellentvoice.co.uk/>

Fat Attitude
<http://www.fatattitude.com> 

Marketing Mania
<http://www.mktmania.com/> 

Qvoice
<http://www.qvoice.co.uk/> 

Rabbit Vocal Management
<http://www.rabbit.uk.net/> 

Rhubarb
<http://www.rhubarb.co.uk/index.asp> 

Speak!
<http://www.speak.ltd.uk/> 

The Joneses
<http://www.meetthejoneses.co.uk/#> 

Vocal Point
<http://www.vocalpoint.net/> 

Voice Bookers
<http://www.voicebookers.com/> 

Voice Works
<http://www.thevoiceworks.com/>

Voice Bank
<http://www.voicebank.ie/> 

Voice Squad
<http://www.voicesquad.com/> 

Vox Talent
<http://www.voxtalent.com/> 

CED Voices
<http://www.cedvoices.com/> 

CAA
<http://www.caa.com/> 
 
You can also contact artists without the use of an agent: 

Several private British professionals are listed here: 
Entsweb
<http://www.entsweb.co.uk/voiceover/> 

Wayne June
<http://www.waynejune.com/> 

Rick Adamson
<http://www.rickadamson.com/home.html> 

DC Douglas - My Voice Over Guy
<http://www.myvoiceoverguy.com/> 

Sctoo Taylor
<http://www.taylormadeproductions.com/demos.html> 

Any Dalaney
<http://www.amydelaneyvoice.com/> 

Paul Meier
<http://www.paulmeier.com/voiceover.html> 

Mitch Collins
<http://www.mitchcollinsvoicetalent.com/> 

Only for your ineterst, I add this article about the current trend in
using voice over talents in commercials, although I think you're not
going to hire Julia Roberts:
Seth Stevenson, "The Voice-Over Gets a Makeover", Slate, 28 March
2005, <http://www.slate.com/id/2115865/>

I hope this answers your question. Please contact me if you need any
clarification on this answer before you rate it.

Above and beyond!  Thank you.

Do you need an accent?  A particular sex?

Is there a cast of characters and you need someone who can play a lot of parts?

Many authors read their own works and do very well at it.

Tony, 

Thank you for the rating and the tip!

Great list, Politicalguru --
I can vouch for voice123.com.  My company has used them in the past and
Tony, you can post a sample of the text and state what you're looking
for and within 2 or 3 hours you will have audio file auditions from
interested Voice Over talent.   It's quite amazing.

More consistently reliable if you want a celebrity, the top Voice over
talent and agencies --  go to
http://www. voicebank.net  
  
Even though the instructions say "register here," you don't have to.
Just click on the link that says "House Reels" and you can listen to voices from
all over the world -- including celebs.  THere are also "narration"
categories and talent that specializes iin "Books on Tape."   You can
also search by name.