Sophie Kinsella is usually funny, her Shopaholic series has recently been made into a film and she has others not part of the series that are good. I've just finished reading Twenties Girl by her and enjoyed it.
Lisa Jewell is also good but her topics can be a bit heavy even though she has the image of a chick-lit writer. Her most recent one, The Truth About Melodie Browne, is hard going but I loved Ralph's Party, Vince and Joy and Thirty-Nothing.
Sarah Addison Allen is an American writer and her books are good and have a bit of a magical twist to them, her characters can do little bits of magic or magical things happen, for example one character has books appear to her when she needs them and another can cook but her recipes have odd influences on people. I've read Garden Spells and The Sugar Queen and enjoyed them both.
Joshilyn Jackson is also a favourite of mine, another American and her books are based in the South. I read Gods in Alabama first and then Between, Georgia and both of them were great. They have strong women characters and funny but dysfunctional families who work things out in the end as supporting characters. Her most recent that I have read is called The Girl Who Stopped Swimming and I recommend it.
Ronlyn Domingue, another American, is good but I've only read one book by her, The Mercy of Thin Air, and it's a ghost story told from the point of view of the ghost.
Vendela Vida has written a couple of good books, Let The Northern Lights Erase Your Name, which I loved, about a woman in search of her natural father, and And Now You Can Go, about a woman in New York whose life changes when she is robbed at gunpoint.
Also you can't go wrong with Carol Sheilds or Anne Tyler (or maybe you can but I think they are both great) I'd recommend Happenstance, The Republic of Love and Unless by Carol Sheilds and The Clock Winder and Morgan's Passing by Anne Tyler.
I haven't read their books but I think Chris Manby is an author similar to the two you mentioned (I love Marian Keyes as well) and perhaps Cecelia Ahearn who wrote PS I Love You. They all seem to be together in the section of the library that has the "If you loved...you might like..." posters.
You might have noticed I love my books so sorry if I went on a bit, recommending books is one of my favourite things to do.
This should be fun..
It was a good movie but the books are better but that always seems to be the case 
