Square

The most popular shape, and understandably so: it's the easiest to fit together into a block, and therefore probably to be recommended if you have a lot of sites to link. There should be something here to fit anyone's style.

• 14 lovely clear icons; taking requests for additions.
• 12 glossy icons in true Web 2.0 style, up to 256x256.
• 30 icons in my favourite set: gradients are interesting without distracting from the icon content. Perfection.
• 30 icons with a slightly metallic matte finish.
• 23 icons up to 256x256, in really fresh colours.
• 13 simple icons with square corners at 50x50.
• 65 icons in yummy wet colours: just lovely.
• 154 icons in lovely black and white: this could be the only set you ever need.
• Marcofolio's set of 25 stamps is a nicely informal take on the square shape.
• There are 65 icons in Studiom6's set , so many logos you won't see anywhere else.

Circular

• Gorgeously simple, 17 icons up to 128x128.
• 154 black-on-white icons up to 256x265. Just about everything you'll ever need.
• 12 "turned over edge" icons up to 128x128.
• 108 black and white round icons: just gorgeous.
• 25 slighly domed-effect icons, up to 256x256
• 19 wood-effect icons in 70x70 and 40x40; I don't normally like wood-effect on the net but these are quite cute.

Cubes

• 5 sites only; 3 versions of each one, but very, very nice.
• 6 sites might just be the ones you need, or inspire you to make your own.

Heart

• 22 heart-shaped icons: nice job that pushes the icons to their limit rather than tidying them up with white space.
• 12 glossy hearts: Web 2.0 graphics with a hearty twist.
• Chocolately heart goodness that might work with any luxury-based theme.

Alcoholism

What can I say: these icons refresh the parts others can't even reach.

• 26 pretty bottle tops from Tydlinka.
• 14 grungy bottle tops by Lenka Meleakova.
• Fancy a glass of Twitter or a pint of Facebook? Very innovative.
• If a tinny's more your style, here are 28 of them from Icontexto.

Stars

• 26 icons: though they tend to lose the logo - stars aren't very conducive to being anything other than stars - they could work well if you only want to use a couple together.

Free Shapes

• Juan Pablo Armstrong's 12 icon set has Colour Lovers and Deviant Art, and has strong cohesion while largely leaving the logos alone.

Hand-drawn

I'm surprised how much I like these: I thought that "hand-drawn website" thing had been and gone, but now I'm having sneaky ideas about a WordPress theme based around a hand-drawn Kubrick. If anyone can draw and fancies a collaboration on this, gimme a shout.

• Mfayaz's set has 22 icons - and seems to be taking requests for additions via comments. Stylistically they're a nice compromise between informal and non-scruffy.
• The G Force's set of 18 icons have super-saturated colour that oozes off the screen: more icons are promised.
• Janko's Handy Icons 2 pack has 21 square icons including PayPal and Skype in a painted finish.

So which do you pick?

You pick the ones you like, of course. But some more thoughts that might influence your liking:

• Square icons are nice if you're using a lot, because they fit together in a block.
• Non-standard shapes are always risky, and the further the graphic is from the standard logo, the greater the risk of it not being recognised.
• The more icons you're using, the more you need a standard shape - probably round or square.
• If you only have one or two icons, you can afford something more quirky that your readers have to give a second glance.