Search for "art" on the web and you'll find that almost every gallery in the world has a website. You're exhausted before you get started.
If you're not used to searching the web, www.teacherxpress.com is a good place to start, offering a collection of useful sites. Then there are heaps of search engines to choose from. I prefer www.google.com - it's clean, quick and you're not bombarded with ads.
Go to www.artcyclopedia.com for a fantastic search engine for fine art. Type an artist's name in the search box and you get a list of images in online galleries. This is a good way to get to know new gallery and museum sites, without having to negotiate your way around them from scratch. At artcyclopedia you can also search by subject matter and so compare styles of a particular genre, such as still life. Search for motivational posters, and you get a series of images inspiring excellence, ambition, imagination, play, risk, successI The bad news is you're sent to a site that sells posters (they're not expensive), but you can print them out to use as starting points for some artistic PSHE work.
You might be surprised and inspired by what you find; I came across www.metmuseum.org when searching for Georgia O'Keefe, and then found I could enlarge an image and zoom in on a detail. Print a collection of images and details - matching the detail to the original is a good starting point for looking closely at a painting. And it's a good way to explore how the artist uses the medium without pressing your nose up to the original.
As well as being useful for class work, internet print-outs are a cheap source for collage work, making an inspiring change from those tatty newspapers and magazines lurking under the classroom sink. Paste a detail from an interesting image on to cartridge paper and work on it and around it in a variety of media.
Of course, you don't need to rely on fine art as a starting point - photographs of people or characters can be cut up and added to in cartoon style, with speech bubbles or captions, to make agitprop posters or story illustrations. Think David Beckham's head stuck on to black paper, with a cartoon body drawn and coloured in on white, a speech bubble demanding protein "to build up my lovely muscles", mounted and displayed as one in a series, and you've got an art project demanding wit, concentration, motor control skills and a class of delighted children (you can't do better than that).
Try www.imdb.com for film stars, www.soccermemo.com for footballers, and search on www.google.com or your favourite search engine for others. Searching for images to work from is a good way to spend a lesson in the computer suite.
The internet is also a good source of how-to-do patterns to link art and geometry. A search for Islamic patterns will throw up many sites with step-by-step instructions; choose those which suit the experience and abilities of the children you teach.
Celtic knots are also an apparently difficult type of pattern, but sophisticated designs can be developed on graph paper, utterly satisfying for children, and then finished beautifully. Go to www.craytech.comdrewknotworkknotwork.html for a good starting point.
A teacher at the primary forum (www.tes.co.ukstaffroom) suggested a visit to http:easyweb.easynet.co.ukiany patternspatterns.htm as a source of naturally occurring patterns. Be warned though - once you sit down for a look you'll be glued to the screen for hours; there are enough sources here to keep you going on a pattern topic for a term.
With the emphasis on international events this year, there are a lot of flags around. There's a complete collection of national flags at www.flags.net - I wish I'd found it years ago. Once every child has chosen hisher preferred flag (the UK has dozens), you have the start of an art and design topic that can go as far as you like: design a shirt or dress, or a family flag that accounts for various national connections; take a detail and print a repeat pattern; paint a self-portrait using the flag's colours; and so on.
The internet is most useful as a source of inspiration to work with your creative mind. Just make sure your colour printer is working.