Regular expression for a list of items separated by comma or by comma and a space

Hey, I can't figure out how to write a regular expression for my website, I would like to let the user input a list of items (tags) separated by comma or by comma and a space, for example "apple, pie,applepie". Would it be possible to have such regexp? Thanks!

EDIT: I would like a regexp for javascript in order to check the input before the user submits a form.