1. jslint.com: a Web tool
This is the tool developed by Douglas Crockford. It has a simple Web interface. You copy and paste your code and click JSLint button, it is that simple. The drawback is every time you make a change, you need to re-copy-n-paste and repeat the validation.
2. TextMate bundles:
3. TextMate integration with JSLint:
Stoyan has a nice post with all the detailed instructions. It is a bit complicated than using method #2.
4. Vim integration with JSLint:
Only saw some discussions on Stack Overflow, did not actually try it out.