I'm going to start with saying that if there is a Goodwill near you, start there. The Goodwill in Elk River is just blocks from my home and I go there at least once a week just to get books. The selection is always changing and most of the books are $0.99 - $1.99. Hardcovers are less than $5.
I had to laugh when I saw the mention to Jennifer Weiner, as I had never heard of her until I picked up "Little Earthquakes" at my Goodwill. I highly recommend it.
I also highly recommend anything by Nora Roberts - I just started re-reading my NR books for the 6th time. I never get tired of them. My favorites are the Irish trilogy - "Jewels of the Sun", "Tears of the Moon" and "Heart of the Sea".
If you're into Highlanders or Time-Travel Romances you should check out Karen Marie Moning's Highlander collection which should be read in the following order -
"Beyond the Highland Mist", "To Tame a Highland Warrior",
"The Highlander's Touch", "Kiss of the Highlander",
"The Dark Highlander", "The Immortal Highlander",
"The Spell of The Highlander".
If you're into paranormal there is Christine Feehan - all of her books are good.
The Shopaholic books by Sophie Kinsella are good as is her "Can You Keep A Secret" and "Undomestic Goddess" and her books written as Madeleine Wickham.
Also, not something that you would generally think of but "Arthur and the Invisibles" is a much, much, much better book than it was a movie. Seeing as most of the book didn't make it into the movie. It had my daughter and I laughing until we cried when Arthurs parents were digging holes and falling in them - never even mentioned in the movie!
I could go on and on but it could take weeks!