(WIP as I continue to gather my thoughts)
For the sake of curiosity, I started looking at Lich-Fiends and what sort of effective combinations could be created with the template. I've not come across any particularly interesting threads with regards to.
The typical Lich is a wizard or sorcerer, and are typically built as traditional spellcasters, given the caster level requirement.
One thing that fiends have the ability to really capitalize on is paralyzing touch. I don't often see humanoid Lich's really make this effective. Many fiends have a nice set of natural attacks, and excellent charisma to fuel the DC.
One big potential downside is sacrificing a great con score for con -.
CriteriaNatural Attacks
Good Charisma
Relevant Attack Bonus for their CR/ECL
CL 11 with 5 SLA to qualify for Lich-Fiend, or ballpark that can be CL boosted
Con score that won't be missed
BonusCreature improves already excellent Hide, Listen, Move Silently, Search, Sense Motive, and Spot skills
Create fills immunity gaps with immunity to cold, electricity, polymorph and mind-affecting.
Potential CandidatesPractical Demonkeeping has a nice list to start on
http://www.minmaxboards.com/index.php?topic=6320.0Lilitu (FCI): Nice set of natural attacks to stack with Paralyzing Touch, SLAs & Spells
Pleasure Devil (FCII): Poison Touch to stack with Paralyzing Touch, high CL on SLAs
Half-Fiend (WE): Customized appropriately
Warlock: Eldritch Claws to deliver Paralyzing Attack
Bone Devil: Advance 1 HD, reasonable SLA support, and good skills to support a sneaky attack into a deadly natural attack combo