A friend wants book suggestions. She is really into time travel stories and I don’t know all that many books about time travel. Any suggestions would be useful.
I thought that The Time Traveler’s Wife was actually a pretty good read. It’s not, strictly-speaking, hard Sc-Fi, but it handles the time traveling really well, and its character relationships are pretty touching.
Tim Powers, The Anubis Gates.
I second Skip’s rec and will add Tomorrow and Tomorrow by Charles Sheffield which isn’t strictly about time travel but does involve travelling through great swaths of time and TimeShips by Stephen Baxter which is a sequel/prequel/retelling of The Time Machine by HG Wells.
That’s in my TBR, thanks (probably) to a Doper.
I’ve read and recommend these:
Replay by Ken Grimwood
A Shortcut in Time by Charles Dickinson
Time and Again by Jack Finney
Mammoth by John Varley
A few others, but they were romancey.
The Anubis Gates by Tim Powers is incredible. A ripping yarn involving time travel within time travel, Byron and Coleridge, Egyptian magic, monsters and many other things. It’s really entertaining.
I’ve heard good things about Kage Baker, but I haven’t read her yet.
(On preview I see Hunter Hawk beat me to it. I figured someone would.)
Connie Willis: The Doomsday Book and To Say Nothing of the Dog. The first one is long and emotionally exhausting (and really, really good). The second one is something of a sequel, but is hilarious (and also really good).
Jack Finney’s books, Time and Again and From Time to Time – did I get the order right? The first one is great, and the second one is good if you enjoyed the first one, but not as good. About Time is a collection of his short stories.
Connie Willis has The Doomesday Book (serious) and To Say Nothing of the Dog (hilarious).
If she doesn’t mind reading kids/young adult books, a fairly recent one that I ADORED is Drift House: The First Voyage by Dale Peck. It’s about a magic house that turns into a ship that sails on the seas of time. Sadly, the sequel was not so hot.
Thanks to all who replied. I will pass on your suggestions to her. Thanks, again.
Why are we assuming the OP doesn’t want romance time travel? If his friend does likes romance, there are tons of time travel romance books. My mom likes Lynn Kurland’s books, for example.
One of the best time travel/historical fiction/romance series I’ve read is Diana Gabaldon’s series that starts with the novel Outlander.
I’ll third the Connie Willis suggestion.
The Man Who Folded Himself by David Gerrold is probably the definitive novel about time travel (as opposed to just using time travel as a vehicle to get the protagonist into a particular milieu).
My favorite is probably the classic Lest Darkness Fall by L. Sprague de Camp.
Not exactly time travel but “The Confessions of a Max Tivoli”-who is born at the age of 70 years old and ages backwards.
Slaughterhouse Five
Heinlein’s The Door Into Summer.
Phillip Jose Farmer’s Riverworld series, while not about time-travel per se, is about the coexistence of people from different times.
“The Proteus Operation” by James Hogan, deals with a group of people trying to go back and help Hitler win the war.
Seconded.
There are, and I like them too. (Green Darkness by Anya Seton, and Melanie Jackson’s stuff)
But how many times have we seen a general book rec thread where someone says “I need something to read, but no romance or westerns, please”? They usually add “no SF” too, but since the OP requested time travel, that didn’t apply this time. 
The Time Wars series by Simon Hawke is pretty fun I think.
Another vote for The Man Who Folded Himself.
The Time Traders series by Andre Norton.