Is there any dierence is traffic to .com sites vs .net or .org? Does one have better search engine results?

[Terry A]

Concerned about the visibility of a new domain registry because.com is not available but .org, .net, .us, ,biz are all available. Wondering if the lack of a .com ending is crucial for potential clients to find us! Thanks in advance!

[Jake]

Technically those example domains are not supposed to have significant ranking differences, realistically because .com is accepted by most users as the standard, you find .com TLDs most often the top in search result, this may be in part due to .com owners investing more effort than the 'also ran' variations.
If the .com of what you want is parked or otherwise underutilized, you should be able to get your alternate TLD to rank first. (You will just always have to include the extension when the site is mentioned in conversation, while a .com can leave off the .com part when discussing the site.)

There are TLDs that get poorer ranking, because .info domains are often offered for a big discount in the first year, some believe such a site can take an additional year to get good ranking (after you have demonstrated the intent to stay around), 2 character TLDs, like .tv are country codes, it's possible that search engines give them favorable ranking for their home countries.
Free domain names are often search ranking poison, recently Google removed all 11 Million .co.cc sites from their index after observing a high frequency of fraud from these easy to get, poorly managed TLDs.