Veterans and Dreadnoughts. The information from both of these, comes out of the latest White Dwarf.
via jullevi over on Warseer
Company veterans (4+1 models, with up to 5 additional)
Any model: Chainsword
Up to three models: Storm bolter, Combi-weapon, Power weapon, Lightning claw, Plasma pistol, Power fist or Pair of lightning claws
Any model: Combat shield, Melta bombs, Storm shield
One in every 5 models: Flamer, Melta gun, Plasma gun
One model: Heavy bolter, Multi-melta, Missile launcher, Plasma cannon or Lascannon
Dedicated transport: Drop Pod, Rhino or Razorback
via Faeit 212 from a source that wants to remain anonymous
Something that was missed for veterans above and some more Dreadnought options
Veterans
Can take flakk missiles
Dreadnought (elite choice)
Can take a drop pod
Can replace its multi-melta with
Twin-linked Autocannon
Twin-linked Flamer
Twin-linked Heavy Bolter
Plasma Cannon
Assualt Cannon
Lascannon
Can replace its other arm with
Missile Launcher
Twin-linked Autocannon
Can replace the built in storm bolter with a heavy flamer
Can be upgraded to Venerable and if does it gets the special rule,
Deathwing Vehicle