User Agent of any browser

http://www.useragentstring.com

Can then be used in Rcurl:

require(RCurl)

require(XML)

webpage <- getURLContent("http://www.useragentstring.com", useragent = "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_1) AppleWebKit/537.73.11 (KHTML, like Gecko) Version/7.0.1 Safari/537.73.11")