This is hard because I keep thinking of more examples and I have little basis for comparison between them, but…
Aurora Leigh in Aurora Leigh by Elizabeth Barrett Browning
Sula Peace in Sula by Toni Morrison
Helen in The Tenant of Wildfell Hall by Anne Bronte
Edna Pontellier in The Awakening by Kate Chopin
Mysteries
... in their way offer a host of master sleuths who happen to be women…
Fantasy
Tolkien offers several not-(or-not-mainly)-romantic very strong women (Éowyn), especially if you count elves (Galadriel)... though they don’t get center stage for long.
A Song of Fire and Ice / A Game of Thrones has many very strong women who aren’t primarily (or at all in some cases) love interests, and several of them do get their own protagonist threads.
Shakespeare has quite a few strong female characters – though they’re often love interests too, I think they stand out as most notable for their strengths, e.g.
Rosalind, the protagonist of As You Like It (clever rebel)
Portia in The Merchant of Venice (though suited by many, and marrying the title character, she then disguises herself as a lawyer and cleverly saves his life)
Cordelia in King Lear
Lady MacBeth (. . .)
(several others)
Sci-Fi:
Honor Harrington is a series of sci fi military books where that character is typically using her tactical brilliance and other skills to reverse overwhelming odds.
Mythology:
Most of the pre-Christian (and even post-Zeus, but especially pre-Zeus) goddesses and demi-goddesses are certainly characters of awesome strength…