Most of the helmet mounts all fit into the standard mount used on a MICH or the basejump molded mount. The ones that don't are the older style Wilcox and the Norotos "Shroud"
For the MICH helmet mount, go with a USGI MICH Plate,
Norotos Universal Shroud, or
Wilcox L4 One- Hole Shroud (if it's 1-hole) or Norotos Universal Shroud or
Ops Core VAS Shroud (if it's a 3-hole).
As for swing arms, if you want cheap get a USGI Rhino Arm off the EE. Otherwise, a Norotos AKA2 or INVG, or a Wilcox L4 G24.
If you go with the USGI, get a USGI J-Arm.
If the
AKA2, it come with adapters for the USGI J-Arm, as well as the
Norotos Dual Dovetail Adapter. (I highly recommend going with the Dual dovetail adapter)
If the
INVG, you'll need the
Norotos Dual Dovetail Adapter
If you go with the
Wilcox L4 G24, you'll need one of the 2 Wilcox Arms
Wilcox Arm w/ Auto shutoff or
Wilcox PVS-14 Arm
It really comes to how much you want to spend. If you don't have a ton of cash the USGI stuff is alright, and you should be able to pick up all 3 pieces (MICH/ACH plate, Rhino Arm, and J-Arm) for ~$100. However, I have a Norotos Universal Shroud/AKA2/Dovetail Adapter setup and it's light years ahead of the USGI stuff.