I've read it many, many times. This probably isn't surprising. I first read The Hobbit at a very young age, but The Lord of the Rings wasn't in the kids section, and it was intimidatingly long, even for me. But when I was a little older — I think 10 — we traveled to Scotland, where my mother grew up. On the way, we visited my mother's cousin Nigel, who (reading my semi-formed taste astutely) strongly recommended two works to me: LOTR and The Hitchhiker's Guide to the Galaxy. Both got their hooks into me good and hard, both get read over and over again and always will, but while Hitchhikers led fairly directly to my first Real Date With A Girl in high school, LOTR has occupied my mind more fully over the years than any other book.
I didn't have a chance to buy the books until we got to Edinburgh. Both were purchased, as far as I can remember, at the John Menzies on Princes Street, near the Scott Monument. It didn't escape my 10-year old self that the Victorian Gothic spire, stained black from years of coal soot, looked more than a little like Robert Garland's painting of Barad-Dur on the cover of my one-volume Unicorn edition of LOTR.
I read great chunks of it all the way across Scotland.I don't remember much about how I read it then, except that I enjoyed the prologue, skipped the songs and poetry, didn't really notice the appendix, but was entranced by the maps. I think most 10-year-olds are miniature cartographers at heart. I know that the transition from the early chapters, so like The Hobbit, and the epic later chapters, was intense. I know I bogged down in the Frodo/Sam/Gollum chapters of The Two Towers — so much so that I lost our car keys in them, triggering a frantic attempt to find an open locksmith in the small Scottish coastal village of my ancestors. I'm pretty sure Tom Bombadil confused me, but that's true for most everyone.
I've read it again and again over that last 20-odd years. At least once every two years, sometimes once a year. Mostly that old Unicorn edition, due to affection and the ease of flipping back and forth in a single volume. I did read the three-volume set at the library a few times, mostly because of the superior maps. My favorite edition, the 50th Anniversary edition with the Alan Lee plates, I don't even own. (As far as I'm concerned, the holy trinity of LOTR artists are Lee, representing the modern era, Garland in the middle, and the old Barbara Remington covers as the classic era.)
As I've read and read again, the scope has increased. The poems and songs get read. The Silmarillion gets (slowly at first) absorbed. The historical appendices, which contain what are now some of my favorite stories. I picked up an encyclopedia, and the first Book of Lost Tales. At this point I even go over the linguistic history, though the languages themselves aren't yet compelling. There's no real end to this, that's part of the pleasure — Tolkien's creation (and his son's collection and arrangement of it) are vast enough, and the world of Tolkien scholarship is probably larger than any other genre creator, with only the Sherlock Holmes folks coming close. I'll ignore the movies and games, not because they're unimportant to me, but because they represent something totally different.
And then, the internet. LOTR fanatics and the net have always been a comfortable match, for obvious reasons, but the resources available now are amazing. The LOTR wikipedia entries are a match in size and complexity for a small nation, and the more individual Encyclopedia of Arda can supplement where terse wiki-knowledge leaves off.
The real find for me, though, is Kate Nepveu's ongoing re-read at Tor.com. It's a slow, chapter-by-chapter re-read of the whole book. Her essays are lovely — she's the perfect critic, someone who is knowledgeable but not expert (allowing her to be surprised at some turns of the narrative), and affectionate but not worshipfull. She's also been drawing in some of the more important works of criticism into hers, leading to (for example) a discussion of LOTR and Augustine. The very best part of these essays, though, are the comments — the commentors are civil, literate, and an interesting mixture of relatively naive readers and those with vast expertise. I'm a geek, but I'm also a former literature major, and it's fascinating to read other folks who can deal with the text seriously, as a fantasy work and on it's own terms, but also draw back and look at it as a work of literature. They've just about finished with the first half of the first book, so there's plenty of time to join in.
I'm doing the re-reading with my old Unicorn copy, but I suspect this is the last time for it. It's stood up bravely to two decades of abuse, but I think it's hit the limit. It will get retired to the top shelf of a bookcase, and maybe I'll grab one of the Alan Lee editions to take the hit for the next few decades.