You can make a start with the free port scanner provided by Security Metrics.
They offer two flavours of scan, either home or business.
Home
- Quick Port Scan of 22 ports
- Immediate results
- Security recommendations available via email
Business
- For Webmasters, Network Administrators, and Executives - test up to three servers.
- Comprehensive
- Port Scan - 65,535 TCP ports & many UDP ports
- Thousands of Vulnerability Assessment tests
- Mail Proxy test for open relays
- Test for hundreds of default username/passwords
- Website html spidering for XSS & other leaks - Email notification when the tests are completed
- Upon authentication you will receive complete vulnerability assessment results
