Second-in-command

The second-in-command refers to a Transformer whose status is...well, second to the commander's. A Transformer who is second-in-command is not necessarily ranked Sub-Commander, while a Transformer ranked Sub-Commander is usually the second-in-command. The rank generally varies between factions. For the Autobots and the Maximals, the rank is usually overlooked, but it still receives its own holiday. For the Decepticons, choosing a Second-in-Command is a very tough decision. Pick one too loyal, and everyone will ignore him. Pick one too bold, and the leader may find himself scrap.

Autobot seconds-in-command

"I...want him to take command......"
Prowl:"What?! NOOO!!!"

Sub-commander

• Grimlock
• Prowl
• Jazz
• Jetfire (Unicron Trilogy)
• Ultra Magnus

Lieutenant

• Blacker
• Lightfoot
• Jazz
• Jazz (Movie)
• Prowl - Lieutenant of Sentinel Prime
• Red Alert (Armada)
• Slingshot

Miscellaneous

• Grandus
• Ironhide
• Sky Garry
• Waver - Second-in-command of Multiforce
• Ratchet (Animated)
• Jazz (Animated)

Decepticon seconds-in-command

• Cyclonus
• Leozack
• Scourge (RID)
• Soundwave
• Scorponok
• Starscream
• Starscream (Movie)
• Starscream (Animated)

Maximal seconds-in-command

Sub-commander

• Apache
• Rhinox
• Triceradon - Dinobot sub-commander

Lieutenant

• Longrack
• Mach Kick - Former lieutenant of the Thoroughbred Corps

Miscellaneous

• Cheetor
• Rattrap

Predacon seconds-in-command

• Dinobot (BW) - Original second-in-Command to Megatron before he joined the Maximals.
• Guiledart
• Gelshark
• Inferno (BW) - Sub-commander (after the death of Scorponok)
• Megastorm
• Scorponok (BW)

References

From Teletraan I: The Transformers Wiki, a Wikia wiki.