A "real one" or an internet one?
You'll find maps in practically all editions of LoTR available, some even have really big ones.
There are also really beautiful maps available made by John Howe, you can find them in most bookshops - there are Beleriand&theNorthernLands, Middleearth as it is in the Third Age and one map with just Wilderland/Rhovanion&Northern Mirkwood. In the boxed set, there's also one of Númenor ^^
One of the official posters for the third movie was an excellent map as well, it's still available in most poster shops.
There are even some books full of maps with very detailed information; the best one of them is imo Fonstad's "Atlas to Middle-earth"
If you are looking for online maps, you'll find quite good ones in the other threads about maps:
http://www.killermovies.com/forums/showthread.php?s=&threadid=298282 (several good maps and links to other websites with maps)
http://www.killermovies.com/forums/showthread.php?s=&threadid=21610 (there's just one link in this one)
http://www.killermovies.com/forums/showthread.php?s=&threadid=22889 (maps showing the evolution of Middle-earth to Europe; most of the maps don't really agree with what Tolkien writes, and several parts are pure fiction. Not necessarily reliable)
http://www.killermovies.com/forums/showthread.php?s=&threadid=24351 (again, some links and one directly posted pic)
http://www.killermovies.com/forums/showthread.php?s=&threadid=2727 (mainly discussion, but also a good link)
If you want very detailed maps that are also reliable (except for some spelling mistakes 😛), I recommend this link:
http://www.annalsofarda.dk/annals-of-arda/Maps-index-tables/Maps.htm
... if you want more information about a specific area, just click on the names there and you get a description of the place.
It's very big though, so if you have a slow internet connection 😬 use a different one 😛