There is a wealth of biographical material on Queen Victoria, but the real question: where to start and what to read.
The standard biography -- and what got me into this mess in the frst place -- is Elizabeth Longford's Queen Victoria: Born to Succeed, which was originally published in 1964. Lady Longford's biography is largely considered as an official biography, as she was given complete access to material in the Royal Archives. Unfortunately, most of Victoria's correspondence was burned by her youngest daughter, Princess Beatrice.
There are several other good (thick) biographies of Victoria, who reigned from 1837 until her death in January 1901. I am rather partial to Cecil Woodham-Smith's Queen Victoria from her Birth Until the Death of the Prince Consort, published in 1972. Woodham-Smith died before she could complete the second volume. The first book is a magnificent achievement - and wohaveuld have, I believe, surpassed Longford. I also have great admiration for Giles St. Aubyn's Queen Victoria: A Portrait (1991), which is impeccably researched, and complements the Longford biography.
American biographer Stanley Weintraub is the author of Victoria: An Intimate Biography, which focuses on Victoria's domestic life. This book was first published in 1987.
I would start with Giles St. Aubyn's work, followed by Longford's book, and then the Cecil Woodham-Smith.