I'm missing six emperors and caesars from the beginning of the adoptive emperors to the end of the severan dynasty. Aelius, Pertinax, Didius Julianus, Pescennius Niger, Clodius Albinus and Diadumenian. I try to stay away from themes or sets because I end up paying a lot more for a coin than what it's worth. Last weekend the main seller I go through on
ebay was selling an Aelius, Clodius Albinus, and Diadumenian.

Clodius Albinus, Silver Denarius, struck as Caesar. Rome Mint. 17.20mm, 1.26g. Minerva standing lt.

Diadumenian Caesar 217 - 218 AD. AE-26. Nicopolis, Moesia Inferior. 26.84mm, 14.37g. Rx./ Zeus seated lt.

Aelius Caesar. 136 - 138 AD. AE-As. Rome Mint. 25.99mm, 12.16g. Rx./ Fortuna standing lt.
I won them all at a good price and plan on using them as fillers until I run across better examples.