I have an account with Preferred411.  There's currently over 120 "Valley" ladies listed.  It's pretty easy to get a free 6-month trial period.  I went ahead and re-upped after the trial.  It isn't outrageously expensive..something like $70 for the year.  Personally, I prefer that the ladies I see are diligent in their screening process.  JMO!

I recently joined Preferred 411, too. And it's already been a benefit for me. You can choose to submit 3 providers for references or have them do a background check which they discreetly do through your employer. I was in a hurry to get it done so I chose the employer background check. It was pretty intrusive, especially having to submit a DNA sample! It's really easy and quick for the lady members to verify you so I think they're worth the $69/yr. It's recognized pretty much nationwide. I also belong to a regional verification site back in my home state which works nicely for the local and visiting lady members.

both P411 and Date-Check, and they have both worked very well for me. Yes, they do verify you on both of these sites, but I have heard of others that are a scam, so be careful.

I saw an ad for a provider that asked me to go to some obscure site, and it was clearly a scam.  I gave them my CC information, and they just sent me round in circles without ever letting me get in contact with the Provider.  I was a fool, and it was NOT easy to cancel the so called service.  
It sounds like the sites others have mentioned are the way to go.  Don't be fooled, as I was, by sites no one has ever heard of.