isn't exactly what you're asking for. It's a standalone application that can integrate with IE, Firefox, and other browsers (including Chrome).
A couple of things it can do, though I haven't used them so I'm not sure how well they suit your request are:
1) Grab a list of all links on a website which lets you select which ones to download.
2) It has a site explorer which lets you view the folders structure of a web site and easily download necessary files or folders.
EDIT: I just found this on the features page (emphasis added):
You can download whole web pages or even whole web sites with HTML Spider. The tool can be adjusted to download files with specified extensions only.