There's a Dark Angel Character that, amidst typical SM goodness, provides a 4+ invul to a unit he joins. A Mob o'30 boys, with a Nob and as many attached characters as you can swing with Klaws or Burnas... Lots of choppy goodness.
Hmm... an IG Primaris Psyker is a lv1 Psyker that has a useful shooting power out of the Codex, or access to 2 rolls on the rulebook powers, other than Divination. He's pretty cheap compared to most other Psykers. He's got a force weapon...
Mephiston, from the Blood Angels, costs as much as a Land Raider, but is basically a high-end Monstrous creature with psychic powers and a built-in option for a "jump pack".