Nothing is better than getting some big groan-worthy guy for cheap, and the best part is since the grave is public your opponents see it coming!

I've got a Sidisi, Brood Tyrant commander list, and some of my favorites are:

Archon of Cruelty: Classic value dude. Gets you stuff immediately, hits for 6 in the air, and continues to cause problems every turn he's alive. He's usually the best option.

Ancient Brass Dragon: Reanimate a Reanimator! Honestly kinda slow, not to mention inconsistent, but I got the extra large Bauldurs gate d20 and it's just so fun to roll!

Dreadfeast Demon: what if my zombies were demons instead? Obviously requires some work to make sure you have fodder, but even if your entire board gets eaten having a board full of 6/6s with evasion is a pretty good spot to be.

Graaz, Unstoppable Juggernaut: But what if instead of demons, they were Juggernauts?? Transforming everyone as soon as he arrives makes Graaz a big aggro play, and depending on boardstate may take out a player or two on the same turn. I've even had the "can't be blocked by walls" text be relevant (take that fog bank!)

So what are your favorite bigguns to bring back from the dead?