Can I show (on my website) logos and names of Companies whose employees use my web-based software?

Your question was asked and answered.

http://www.avvo.com/legal-answers/can-i-claim-that-a-company-is-my-customer-and-show-151034.html

People who buy things using their email addresses expect to remain anonymous, and they haven't consented to having their names and work affiliations used in the vendor's advertisements as de facto endorsers of your software. Also, the facts that they bought the software doesn't mean they're actually using it - it could have been a gift, or it could be that they want to use it in their work as an example of bad software. So you need their consent.

The companies may not appreciate your free advertising - trademark rightsholders are the ones who get to decide whether a use is damaging to their brand, not the unauthorized user. YBut your use isn't as a competitor and is only to nominatively identify the employees by their work affiliations, so while using the ompany's logos rather than just their names might be pushing it, I think it's ok if the employees/customers consent .

Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.

You are overlooking one critical piece of this analysis; Privacy Rights and Privacy Policy. The information that you want to display (email, names, etc.) is generally considered as "personally identifiable information" throughout the world. As a result, there are various laws and regulations (some that are international, such as the EU) that cover the disclosure of that information to the public at large. You should consult your own privacy policy to see if that type of disclosure is permitted by your own registration terms. Most such policies do not allow such disclosures and as a matter of business practice (and you sould ask yourself if doing this might actually hurt you in that users who are aware this might happen will decline to sing up in the first place), if you intend on doing this your users should be informed in writing. Looking at the models of other online operations (though given the facts here I am not sure if this is wholly analagous), most will not reveal the actual names of the users (e.e., salesforce.com). Their site privacy policy provides:

"Salesforce.com does not share, sell, rent, or trade personally identifiable information with third parties for their promotional purposes. Salesforce.com may share information collected with other companies that work on Salesforce.com’s behalf."

I hope this helps and if you need to cosult with our office, please feel free to reach out to us.

Disclaimer: This answer is for informational purposes only and does not constitute general or specific legal advice, nor create an attorney client relationship.

No, you cannot.
You can list the name of the company, but cannot use their trademark without their express permission.