Something you've probably noticed on the Haven is that there is no gallery or media section. This is deliberate. I decided a long time ago that most images of Harley were very prolific on the web and I'd mostly be just reproducing them. With the growth of youtube, there's multiple clips you can now find on Harley and Joker as well.
Some of the other Harley websites have lots of images and clips and their links are provided below as well.
But do a google image or a youtube search for Harley Quinn and you will turn up heaps of stuff!

Google Images
Youtube

Harley on Wikipedia
A really good outline of Harley!

Harley's Homepage
This is it, kiddies - the FIRST HQ website on the internet, and still up! This was the site that first gave me access to the much desired and craved Harley info when I was so cut off from everything here in Oz. I ADORE this site!

Harley Quinn
Another long-running HQ website. Sadly, not updated in a very long time, but still worth a look!

HQAA
An awesome archive of Harley images!

Collecting Harley
A truly neat 'n' clean and utterly spiffy HQ website with some great information, well presented and clear.

Harley's Heaven
Another fabulous long-running website with heaps of cool stuff. Check it out!

Joker x Harley Fanclub
Fanart drawn by those fans who love the wonderful pairing of JokerxHarley!

Harley's Quinn's livejournal community
A LJ comm dedicated to the ebullient Miss. Quinn herself!

Joker x Harley livejournal community
Another LJ comm dedicated to the pairing. Don't forget to check the 'memories' section of this community as it has lots of great info there for you to sift through!