Also -- despite what you may have learned in school -- the taste buds aren't mapped to areas: http://en.wikipedia.org/wiki/List_of_common_misconceptions (Search for Taste for links to the relevant sources)
Well-known umami-tasting foods include red meat, cheese and other fermented products, and tomatoes. None of these contain MSG directly (tomatoes get their umami from glutamic acid, according to umamiinfo.com). However, MSG can be used to add more umami flavour, which acts as a flavour enhancer.
"MSG is the sodium salt of glutamic acid"