Important Transport layer ports

20 - First - FTP - File Transfer Protocol - Data 

21 - First - FTP Control messages

FTP is exclusive to TCP, since connection should be established before Data getting transmitted.

22 - Second - SSH -Secure Shell

SSH can run on both TCP and UDP. TCP is default setting.

23 - Third - Telnet

Telnet strictly uses TCP, it cannot be used on UDP.

25 - SMTP - Simple Main Transfer Protocol

53 - DNS - Domain Name server

DNS works on UDP

67 - DHCP Server

68 - DHCP Client

DHCP works on UDP, Since there is a broadcast on server reply it is required to use 2 ports separately for client and server to differentiate origin of message.

80 - HTTP - Hyper Text Transfer Protocol

443 - HTTPS - Hyper Text Transfer Protocol Secured

HTTP generally runs on TCP, however it can be implemented on UDP as well.

161 - SNMP Agents

162 - SNMP Traps

SNMP uses UDP

520 - RIP - Routing Information Protocol

RIP uses UDP on transport layer

143 - IMAP - Internet Message Access Protocol