A few helpful places to go for ideas for Advent and preparation for Christmas:
Celebrating Advent in the Home: lovely simple leaflet with daily advent readings, and a liturgy for candle lighting. Also some good resources on a Jesse tree and Advent Wreaths. Excellent.
Christmas Wrapped Up and More Christmas Wrapped Up: a couple of volumes of resources produced by Scripture Union, with dramas, readings, word searches, craft activities, and a whole host of other things. Almost impossible not to find something useful.
Barnabas in Churches Ideas Page: a great selection of resources on the Chrisitan year, as well as a host of other themes, posted by a collection of folk around the country.
A Holy Christmas positively heaving with links to advent and Christmas resources, some links now out of date, but an incredible collection.
Advent Wreath prayers from the CofE liturgical commission.
Childrens colouring pages & wordsearches. Quite remarkable to find a US site which was offering this stuff for free. Seriously.
ReJesus have some online meditations.
The Churches Advertising network has a couple of good radio ads to go with the excellent nativity cartoon they created.
Silent Night by John Birch, available to download from Proost
Advent Meditation, discovered via Bishop Alans sidebar.
Video and photo resources from Reelworship. Simple but good quality.
Big collection of sites doing graphics for worship (plus a whole lot else) here, but most of them will charge you. See comment above!
Dave Walker Christmas themed cartoons.
or for something completely different, go to Creative Prayer, which has bags of ideas for interactive prayer stations. Couldn't find much that was directly to do with advent, but that's not going to stop me recommending it.
Finally previous advent resources posts, there's a bit of overlap between them.