This is a list of commonly used ports, and does not include all possible ports that may be opened on a server.
cPanel
cPanel 2082
cPanel - SSL 2083
WHM 2086
WHM - SSL 2087
Webmail 2095 Webmail - SSL 2096
Email
POP3 110
POP3 - SSL 995
IMAP 143
IMAP - SSL
993 SMTP
25 SMTP
Alternate 26
SMTP Alternate 587
SMTP - SSL 465
Web HTTP 80
SSL 443
FTP 21
FTPs 990
SFTP 22 SFTP
Shared/Reseller
Servers 2222
Webdisk 2077
Webdisk - SSL 2078
MySQL 3306
MSSQL 1433
SSH 22 SSH
Shared/Reseller Servers 2222
Other
Plesk Control Panel 8880
Plesk Control Panel - SSL 8443
Plesk Linux Webmail N/A*
Plesk Windows Webmail (SmarterMail) 9998**
Virtuozzo 4643
DotNet Panel 9001
DotNet Panel Login 80
RDP (Remote Desktop Protocol) 4489