"Naman" is one of those Tagalog words that's really hard to translate. It actually changes meaning depending on how you use it.
Tagalonglang.com has a useful page HERE which explains some of its uses. According to the site, the word "naman" can be used to contrast, to soften requests, or to give emphasis."
Matt and I just came from this lesson about answering the question "Kamusta ka?" In the video HERE, the answer provided is "Mabuti naman po." In this context, "naman" becomes "too."
Here are some more uses of "naman" from the top of my head:
Ikaw na naman! = You again!
Naman! (street slang, shorcut of "oo naman!") = Of course! Or, more precisely, "Was there any doubt?"
Adding another idea from AR:
naman eh = when you're getting "pikon" (sige nga, hanap ka ng translation) or when expressing disappointment *P. S. Sorry for the conyo-sounding post
Little brother ("bunso" = youngest brother) = Ate, penge ng candy. (Older sister, give me candy.)
Older sister ("ate") = Wala na eh. (There's no more.)
Little brother (expressing disappointment) = Naman eh. (Still have no idea how to actually translate this.)