Books, books, books! I love reading. I used to read a LOT when I was young. Mom was always surprised to see what I brought home from my elementary school library. I read Gone With the Wind in 5th grade, before Mom took me to see the movie for my birthday. I loved animal stories, and once I found Jack London I read everything of his I could get.
My best friend and I discovered Robert Heinlein when we were in Jr.HS and read every one of his paperbacks we could find. The idea of ESP fascinated us, as well as space travel, computers, and time travel. Heinlein was only the beginning of a life-long love of Science Fiction and Fantasy.
One of my all-time favorite recent SF novels is 'Antarctica' by Kim Stanley Robinson. I have real trouble with a lot of male SF authors' characterizations of women, but he's created some wonderful, strong female characters in this one. And it's funny.
If you want a blend of Celtic history and SF/fantasy, Patricia Kennealy-Morrison is great. My favorites are the books in her later trilogy, the Tales of Arthur, because I like the characters more. All of her books are a blend of Celts-in-space and Celtic legend and history.
Katherine Kerr is another author who fuses Celtic history and fantasy. She uses a non-linear method of storytelling, like Celtic interlace, interweaving the characters' past and present lives. It can be disconcerting at first, but I enjoy re-encountering some of the characters' previous incarnations.
Another two favorites are Mary Gentle and C.J. Cherryh. Both of them have a real talent for creating authentic alien characters, with thought patterns, cultures and behaviors that are different enough to make you believe they're not just humans-in-disguise. And their characters of both genders are well-rounded and realistic.
Some of my other favorite female fantasy and SF writers are Kate Elliott, Ursula Le Guin, Karen Traviss, Marjorie Bujold, and Lian Hearn. I tend to like adventure and exploration over romance, but that's not to say there is no romance in these books. It's just not the main focus.
You can probably find most of the authors I've mentioned on Wikipedia if you're curious about their work.