I think the weirdest I saw was in the film, Somewhere in Time. Christopher Reeve just had to lie down, close his eyes, and wish for it. And getting back? He dropped a 1972 (or thereabouts) Lincoln penny on the floor and the moment he saw it, bam! He was back in the present.
Spoiler You generally seem to be right about Henry's trips backwards through time being confined to his own lifespan - but towards the end he jumps into the future and meets his daughter, who tells him that he died five years previously, and the very last chapter of the book is Henry visiting Clare in her old age, many years after his death.
Vonnegut's Timequake. The universe just kind of resets ten years and everybody on the planet has to relive those ten years on autopilot, with complete knowledge of the future and no way to change it.
Didn't that also involve recreating, in the present, the environment of the period one wanted to travel back to? I seem to remember the experimenters furnished a room in the Dakota Hotel in NYC to look exactly as it would have in 1800-whatever. So the room served as a kind of portal. I liked that book, though I was never sure about the ending.
That's a little like what happens in Seldon Edwards' The Little Book. Only in that case, it was time travel by near-death/pre-death experience, and the doomed MC found himself in fin-de-siecle Vienna.
Were you hoping somebody would tell you this method isn't silly? Okay, I will. It's not silly. Stone circles/barrows/dolmens are weird places, especially if they're on ley lines. Anything could happen there.
Not from a book but a blog, but I figure it merits a mention: Hypertime: an excessively convoluted time travel framework
The Delorean from BTTF. Why anyone would drive such a jalopy is beyond me! On a serious note, I watched Neil deGrasse Tyson demonstrate time travel using molecules and lasers. I forget the science behind it unfortunately (it was a few years ago now!) but it was weird and eye-opening!
Is this related to the idea that electrons actually operate in more dimensions than we realise? I think the extreme version of this line of thinking goes as far as postulating that there is only one electron in the entire universe, and it is constantly travelling backwards and forwards in time.