i got a telescopic and folding one of ebay its called bike tool by union see link. its got a rotating clamp and rubber grips to avoid scratches to the frame and has QR claps to lock the 3 sections together so you can work at any height plus the legs are about 3 feet so its dead stable. ps its not me sellign it! mines about a year old and just found this by searching.
I use the £135 Park one, which I am very happy with. However some people don't like the leaver action clamp, apparently. I always clamp it to my seat posts, which are the same on both my bikes, so it doesn't bother me.
I have also heard/read good things about the £117 Ultimate Consumer Stand, which employs the screw clamp method.
I would definitely recommend getting one if you do your own maintenance and/or clean your bike regularly.
starsky, it only has 2 legs but they spread out quite wide and the have a bar from the tip of the leg to a collar that slides up and down the main tube and locks with a QR and so are pretty stable. for extra leverage you can always put a foot on one leg but for most jobs its fine even when you rotate the bike in odd possitions and lock the clap