I stumbled across an awesome (though not new) website this past weekend called "I Am Not A Stalker." Compiled by actress Lindsay Blake, the site showcases upcoming celebrity events such as movie premieres and book signings so fans know where they can find their favorite (LA) celebrities at various times throughout the months, as well as evidence of filming locations of past television shows and movies.
Highlights include pages dedicated to fan favorites Sex and the City and My So Called Life but some of the more "hardcore fans" will undoubtedly prefer the page about celebrity homes. So of course by "hardcore fans" I mean telephoto lens weilding paparazzo and sometimes sniveling autograph hounds.
Blake all but posts the street address of some celebrities (such as Jennie Garth and Peter Facinelli)'s past and/or current places of residence. When possible Blake poses for photos outside of the locations about which she writes. She also has a section where fans of her site can send in their photos with celebrities they have "stalked" out in LA in recent times.
Blake's site is not the only one of its kind, nor do I think it was the first or is perhaps the most thorough. The latter fact I believe is because she seems to run the site single-handedly despite her "day job" as an actor, whereas sites like On Location Vacations rely heavily on tips from fans who happen to see the telling yellow gingerbreads posted in their neighborhoods.
OLV is a global site. Though it focuses heavily on staple shows for New York City like 30 Rock, Gossip Girl, and Law & Order: SVU, it also posts news on fads and crazes like the Harry Potter and Twilight film franchises. OLV encourages its readers to submit amateur YouTube video of their experience watching shows film in outdoor locations, which often leads to spoiler scoops and rare actors-in-character appearances.
OLV never gets personal with its calendar or events news; all of the information they post is based around the fandom of a show, not a particular actor. They have even recently expanded into posting casting news, new film trailers, and other entertainment marketing materials, marking them as an up-and-coming go-to source for all things entertainment.
You can also follow Lindsay and/or OLV on Twitter for up to the minute "not stalking" information. And I have my own version (albeit an extremely scaled-down version) of celebrities seen around LA in my "Celebrities Who Should Love My Book" column.