Mini Disclaimer: The views and opinions expressed are strictly my own and may not be accurate.
Top Level Domains, or TLDs are the last part of a domain name directly after the last period and include .com, .org, .edu, .net, and numerous others. The important thing to realize when deciding on a TLD is to what purpose your website will have and to choose an appropriate one. This happens before you even begin to consider the SEO aspect of TLDs. If your website is a commercial website, go with a .com, if it is an organization obviously a .org is better suited for you. That being said, the TLD you choose will have an impact. Search Engines such as Google give higher precedence to .coms, .orgs, because usually these websites are owned by physical companies, other domains with .info, .biz, and so on are given less weight, for numerous factors, one being the emergence of cheap domain registration services that offer these types of domains at perspicuously low prices.
For SEO purposes there is much ongoing debate about the ramifications of TLDs for SEO purposes. One side saying that yes they do matter, the other saying quite the opposite. In my experience SEO goes much farther beyond just the end of the domain name and I have seen plenty of .info domains outranking their .com counterparts. It’s all about the quality of the content on the site, how many visitors are going to it, and how many links are pointing at the site.
The other significance of a TLD is the viewers expectations. Most users on the internet are much more use to visiting .com and .org sites and I’d wager that 9 out of 10 times if given the opportunity, the visitor would choose a .com over another TLD without thinking twice. This is of extreme importance when choosing your domain name, as visitors may be subconsciously avoiding the site because of a poor chose in TLD.
This is a darn interesting question, and one that clearly isn’t cut and dry because there’s a lot of debate in the SEO community on this topic. The question is really: everything else being equal, would a “.com” be ranked more highly than a “.cn” or a “.fm” or similar?
My answer: yes.
Of course, since Google uses at least 180 different factors when it calculates Search Engine Results Placement (SERPs), the odds of having two pages with the exactly same score other than domain name seems exceptionally unlikely: if two pages were the same, then the newer file would suffer from some kind of duplicate content issue!
Nonetheless, I believe that there’s also a psychological issue too, and know that I have a higher degree of confidence buying from a “.com” company than a “.cn” or “.cz” company, though I own “.com”, “.net”, “.org” and “.info” domains. No “.mil” yet. 
So if you have the choice between a splendid non-mainstream TLD domain name and a crummy, obscure name that’s a “.com”, I would suggest that you pick the former, not the latter. But then again, I believe that the vast majority of people come to a site because of the content, through search engines, so a human-readable domain might not be that important anyway.
