You can see my site here. The share buttons on the left side obviously look quite untidy... Any ideas on how to make them look better?
An easy way to make them better is to get rid of most of them. Large sites with lots of visitors see Twitter/Facebook in use but not a lot else.
Don't bother with the StumbleUpon buttons because SU people have their little toolbar and are in the habit of using the toolbar for that. Same goes for any other link - people don't click them.
Also consider usability. The buttons need to be in some logical place on the content, not thrown on the page to look like you are all modern what-with-your-Facebook-button-n'all. People expect navigation on the left, you have to go with their expectations. In the top-right is no good either - people will not go looking in blindspots for the 'twitter button'. If you are selling products then by the 'add to cart' button is a good idea as people will maybe think of checking with their other half/friend on some purchase that they may not be immediately wanting to buy.
As they stand now, a simple tweak would be to make them uniformly sized and aligned with each other. Here's how they look with guides visible and gutters highlighted in red-yellow:
You could also add a background around them to make them appear as a cohesive page element and may want to consider using reworked icons that better fit your theme. Some links for inspiration are at the end of this answer.
One of my favorite integrations of social icons is at DanielMarques.me. His site looks like a bookshelf and his icons look like they're sitting on the shelf:
Inspirations: http://webdesignledger.com/inspiration/55-examples-of-beautifully-integrated-social-media-links-in-web-design Icon sets: http://speckyboy.com/2009/01/26/30-amazingly-creative-social-bookmarks-icon-sets/