My favorites are:
Diana Gabaldon's outlander series (the Lord John books aren't bad, but outlander is better)
Stephenie Meyer's Twilight Series (Yes, it's marketed as YA, but the stories and the romance are fab. for any age.) Also liked The Host which is separate from the series.
And I second Marian Keyes, Sophie Kinsella, and Mary Kay Andrews.
For the person who was wondering about Sophie Kinsella writing under the name of Madeline Wickham: I've read her books written as Madeline Wickham and didn't find them as good. They seem stiffer and a little more serious to me -- not as much fun and harder to read because the "flow" isn't there. They aren't bad, but I can see why they were written first and then she changed her name to write the next ones. Madeline Wickham is her real name and I'm betting those first books didn't sell well so when she came up with the Shopaholic series that was better, her agent or publisher told her to change her name to get around earlier lackluster sales. When she hit it big as SK, they re-released the older books to capitalize on her fame. But they still aren't as good, IMHO.