Your most common file extensions will probably be .html, .php, or .asp – Google’s Matt Cutts has gone on record as saying the search engine is happy to crawl any of those pages and it doesn’t really matter which extension you choose of the three. However, he does warn against using extensions such as .exe, .dll, and .bin. These extensions signify mostly binary data, so are largely ignored by the search engine crawlers.
http://www.searchmarketingstandard.com/url-structure-seo