There seems like there are tons of websites for aspiring Voice Over artists. Most promise you big bucks (if you pay them big bucks) or "insider' secrets you could have found on your own if you Googled.
One site that has done a lot for me and some of my friends in the business is VoiceBank.net and it's attached sister site VoiceRegistry. This isn't a site for beginners. This is a site for those that have been at it a bit, have professionally produced demos and a few spots under your belt.
Through this site some of my friends and me have landed agents as they have a huge data base as part of the site, with contact emails and website URLs. A key point made by a friend is don't just click on the email address and send away. The best plan of attack is to click the company's website URL and see what submission process they have (most agents have it listed, along with exact exact submission instructions). That way your email isn't deleted or you're not black-flagged for the inability to follow directions.
One outstanding aspect of Voice Registry is something they call Weekend Workout. You have to be a paying member ($10 a month or $84 for a year) to participate. Each Monday afternoon they'll post a few scripts and announce the "guest reviewer" which is always a top agent or producer. You pick a single script, do your best job recording it and then upload it. The deadline is the following Thursday at Noon, so you have plenty of time. Then, the next Monday, there will be a page with all of the submissions and a personalized "review" of each effort.
The review usually is only a sentence or two...but always some valuable information from the "judge" on what they heard right and/or wrong with your effort. Solid information to improve your craft from someone truly in the know. Recently, the site had the judge actually record a personalized review for each participant instead of a typed response. Pretty cool.
And, while very rare, participating might actually land you an agent. I've seen past reviews where the "judge" ended their review with "if you're seeking representation....". And, I'm pleased to know, first hand, a good friend that recently landed with a very prestigious agency by participating. Sort of like the "being discovered in a drug store" movie star story. True, it's rare (there is probably 120 or so submission each week) but I know it does happen.
Of course, the reviewer may not volunteer interest but could look you up as the site provides space for you to upload your demo(s), head shot and resume. You never know.
To me, this site is great and I highly recommend it. $84 for a year of weekly exposure to the top talent agents and producers is nothing to sneeze at.