Despite they can run on any port, services such as ftp, web, or ldap generally use the ports reserved for them. Port 80 for example is used by web servers for HTTP. Port 443 is the port for HTTPS.

TCP
    20: ftp data
    21: ftp control
    22: ssh
    23: telnet
    25: SMTP (mail)
    37: Time protocol
    53: Bind/DNS
    69: TFTP (Trivial FTP)
    80: HTTP
    109: POP2
    110: POP3
    111: RPC Remote Procedure Call
    137: Netbios Name Service
    138: Netbios Datagram Service
    139: Netbios Session Service
    143: IMAP (mail)
    161: SNMP
    220: IMAP
    389: LDAP
    443: HTTPS
    445: MS Active Directory, SMB
    464: Kerberos
    1521: Oracle Database
    3000: Node JS
    3306: MySQL
UDP
    69: TFTP
    161: SNMP

http://www.0daysecurity.com/penetration-testing/enumeration.html