Space MarinesVeterans - most chapters have a different helmet color designated for veterans
Thunderfire Cannon -
Onslaught Miniatures Grudd stuff
Imperial GuardSupport Sentinels - missile pods from
these plus sentinel models
Bane Wolf - honestly, I'd just use slightly different paint jobs to differentiate the Hellhound types
Devil Dog - ^same
Sentinel Powerlifter - could be converted using a sentinel model and part of a 40K Ad Mech
taser goadOrksNobz -
Skinnerz Commando SpecialistsBurna Boyz - ^same
Tankbustas - ^same
Mega Dreads -
Skinnerz TramplersGorkanaut - these are basically the Epic Stompas, so just add a few bits n bobs here n there
Morkanaut - ^same
Warkopta -
ShapewaysGrot Tank -
Skinnerz Micro Tank Platoon or
Microworld Games Wasteland BuggiesDakkajet - use any combo of planes+bits you want: Vanguard Skinnerz or Novan Regulars, Shapeways historical aircraft, Epic/Aeronautica Imperialis Ork or other aircraft, 40K Stormboyz jump packs, etc...
Burna-bommer ^same
Blitza-bommer ^same
Wazbom Blastjet ^same
Battlewagons - most of the old Epic specialty ork wagons are more properly battlewagon sized,
ChaosRaptors - Chaos Marines +
bat wingsObliterators - buy your terminator proxy of choice, add greenstuff goop and assorted weapon bits
Dreadnoughts - add various bits to a plastic Contemptor Dreadnought
DaemonsBeasts of Nurgle - start with a Nurgling as the base?
Fiends of Slaanesh -
Khurasan Miniatures Space Daemons (aka Alien franchise models), or Warmaster Chaos Hounds (potentially converted with daemonette claw arms)
Seekers -
Microworld Games Raptor Dragoon Cluster + old daemonettes
Screamers - the new Citadel Barbed Bracken kit looks like a great base for making screamers
Furies -
Microworld Games Bat HarpiesChaos Spawn - start with a Nurgling as the base?