https://chrome.google.com/extensions/
You'll need to be running the dev channel version of chrome:
http://www.chromium.org/getting-involved/dev-channel
(summary: uninstall if you're using a non-dev version of chrome, download and run the dev installer, or use the channel changer)
I'm currently using:
- AdThwart - yes, it still downloads the ads, not doing so is on the to-do-list
- FlashBlock
- Google Quick Scroll
- Google Tasks
- Google Translate
- Send from Gmail