Blue force gear sling
Ace M4-7 tube + Magpul CTR
Standard handguard & pistol grip
HK 416 rear sight with XS "AR" style upgrade
Custom battle-rifle front sight
Stanag bayonet lug
Swiss front takedown pin
Lancer L5 mag (for show, any more mags will be the more economical Pmags)
I handled a SIG 556, and all I can say is even with the 551 handguards it still feels nose heavy, but the real kicker for me was you need fingers liek Arsenio Hall to reach the selector and mag release. They seriously screwed the pooch on those ergos IMHO. It had a lot of potential to be my 'perfect' rifle but they ended up fallling short of the mark.
The problems with the 556 can be summed up in two words.
They're pretty much good to go out of the box, but the effort from the factory was lacking. My opinion is that they could have put a rifle similar to this for about the same cost as they currently sell for. Why they didn't is beyond me. To quote one good smith "SIG screwed it up, what everybody wanted was a 55X with an AR mag well".
I got my 416 rear sight from HKparts (Adam) and it's a little bit lower than the standard AR sight (or the centurion arms HK style sight), which tends to be a little high for comfort on the 556. The front sight is a National Match M14. CRT stocks work pretty good and are a natural pair with the Ace M4-7 heavy duty tube.
Best source for SIG parts is Gun Factory (until maybe MFI gets cranking). They have a guy there that speaks English.
Jbrown, hopefully I'll be able to get some trigger time sometime soon.
Addax, thanks for the compliment. Best as I can figure, SIG doesn't have a lot of interaction with the people that use their products (at least on the commercial sales). On an unrelated, but slightly similar subject, ask the guys at Primary Weapon Systems to consider adding a sling mount on their gas blocks in future versions. All us low-speed, high-drag, cheap-shooters want a piston conversion, but the cost of the conversion + necessary rail is $700 in addition to whatever we paid for the original AR, and there's no getting around it. Brings the end cost of the product up there with the monolithic LMT piston, and a few other piston rifles.