Common ports in my mind

Common ports

• 
   21 FTP
• 22 SSH
• 23 TELNET
• 25 SMTP
• 53 DNS
• 80 HTTP
• 110 POP3
• 115 SFTP
• 135 RPC
• 139 NetBIOS
• 143 IMAP
• 194 IRC
• 443 SSL
• 445 SMB
• 1433 MSSQL
• 3306 MySQL
• 3389 Remote Desktop
• 5632 PCAnywhere
• 5900 VNC
• 6112 Warcraft III

Open Port Check Tool

The open port checker is a tool you can use to check your external IP address and detect open ports on your connection. This tool is useful for finding out if your port forwarding is setup correctly or if your server applications are being blocked by a firewall. This tool may also be used as a port scanner to scan your network for ports that are commonly forwarded. It is important to note that some ports, such as port 25, are often blocked at the ISP level in an attempt to prevent malicious activity. 

http://www.yougetsignal.com/tools/open-ports/