Virus Total- Analyzes the file you provide with a dozen of anti-virus programs. I use it to scan our installers.

These tools will let you see if Google has any problems accessing your pages.
Google Cache Checking Tool
Checks whether URL(s) have been cached by Google and the date they were cached.
Search Engine Spider Simulator
Lets you see through the eyes of spiders.

I’ve just played with DomainsBot. The bot takes synonyms into account when searching for domain names. Nice results. Really helpful when you need an idea for your domain name.