BY THEM NOW
also buy the rest of the books concerning Tolk. you won't regret it.

Definitely buy and The Silmarillion and Unfinished Tales, but don't rush into buying the ten volume History of Middle-earth series, as it is basically a reference set and much that you will find there is apocryphal and doesen't make for a good read, as in a good adventure story. IMHO. Look through the H.O.M.E. threads to find a list of those volumes that you might find interesting.

UT is definitly worth it. if you loved LotR and the Hobbit.... UT is sooo worth it. it builds on everything else. i tried to read it before the silmarillion and it just didn't work. if anything... make sure you read it after the others. it will deepen your understanding of tolkien's world.
you'll never regret buying UT.... trust me...

and yes.... burn harry potter...

Grimbledore? Thta's outrageous!!!!!

Yes on UT, but let's not get ahead of ourselves: I've said it before and I'll say it again, one CANNOT fully appreciate TLotR without the Silmarillion. Completely ignoring the references to Gil-Galad (which, sadly, is about all we EVER get) and Earendil, the poignancy of what is irrevocably gone and only a shadow fading fast in the Trilogy requires the Silmarillion to understand. To say nothing of the fact that, once again, Feanor could've (and certainly would've) kicked Saurons tail up one side of ME and down the other one.

If you've read LotR, the Hobbit, and Unfinished Tales, the next I'd recommend would be the Silmarillion; it opens the door to a broad expanse of history that you only saw glimpses of in LotR; after reading it, references in LotR to the Elder Days will make much more sense. The language is beautiful though sometimes hard to get through. I will be honest: it is not as easy to follow as LotR; it is not through one viewpoint, but rather a collection of stories. Rúmil, a Noldo of Tirion, wrote the Ainulindalë, and Pengolodh compiled the Quenta Silmarillion. Dírhaval wrote the Narn i Chîn Húrin, and Elendil wrote the Akallabêth. If I remember correctly, these tales of yore were part of what Bilbo added to the Red Book in his Translations from the Elvish.

There wasn't one in my 1988 Del Rey paperback edition, which only had the three 1988 maps of Númenórë, Middle-earth, and Gondor/Mordor by Shelly Shapiro. Nor was there one in my 1980 Houghton Mifflin large paperback edition.

I recently reread the UT at the urging of a leggy blonde ('cos I just can't say no, sigh) and was amazed by all the stuff I'd forgotten. UT is the only place of which I know where we learn WHAT the Seven Gates of the City of Seven Gates were, and even see Sindarin archers who followed Turgon from Vinyamar guarding one. I wanted to knock the #@!$ out of Aldarion and Erendis, plus there's the only account (sort of) the formation of the alliance between Gondor and Rohan and some interesting stuff on the mechanics and use of the Palantiri (was Denethor a Warden of the Minas Tirith Palantir even while his father lived? It seems likely.)