Just a size comparison of the sprites I'm working on, done or otherwise. The characters so far include:
Optimus Prime, Megatron, Nemesis Prime, Bumblebee, Goldbug, Cliffjumper, Ironhide, Ratchet, Jazz, Bluestreak, Smokecreen, Prowl, Windcharger, Ultra Magnus, Soundwave, SoundBlaster, Starscream, Thundercracker, Skywarp, Wasp, Car Drones and plane drones, Hot Rod, Rodimus Prime, Galvatron, Hot Danimus, Danimus Prime, Bulkhead, Captain America, Op-Thomas Prime, a modernized Optimus Prime, Antronus, and Novatron.

The list will improve with each new characters and changes, so expect more.

Transformers(most of them) belongs to Hasbros
Captain America belongs to MARVEL
Thomas the tank enging belongs to HiT Entertainment
Opthomas Prime belonged to James Farr
some Transformers + sprites belongs to me