Cosmic J:
I like the Raiden and Shinden Armor from Gasaraki - but they're out of production and hard to find at a good price. If you can locate them, they are worth the effort.
The Votoms series has some interesting armor designs. The 1/20 Scopedog comes in two versions: the plain vanilla kit, and the special boxing w/ photo-etch parts.
Well, I don't know if 4-meter mecha really count as "powered armor suits"... But Hobbywave has the Gasaraki kits. Pricing is pretty reasonable, too. I thought about buying some more to boost my collection but decided against it.
And there's more variants of the Scopedog, naturally: Red Shoulder Custom and Pailsen Files versions from Bandai, and Wave's line-up includes other stuff like the Turbo Custom and the parachute type... Not to mention Bandai's Fatty and Takara's line-up of the other mecha from the show...
Centurion: You say you're not interested in the anime-looking stuff but would prefer more MaK or Mechwarrior-type stuff... I think I get what you're saying, it sounds like you want stuff that looks more like machines and less like cartoon super-robots. But it always seemed to me that the "MaK look" was mostly a matter of paint schemes. The MaK stuff was originally kitbashes and stuff, after all, armor pieces cut from ping pong balls, etc.. it was mostly the paint schemes that gave them the gritty look for which they're known. So there may be a larger selection of kits that could fit your needs than you might at first think.
I can't really recommend any other powered suit-type kits besides what people have already suggested: but here's a few more mecha kits that might appeal to you:
- Sunshine: There may be other Armored Core kits that might suit your fancy as well, I don't know. But "Sunshine" has kind of a modern-AFV aesthetic to it, so I thought it might be one to consider.
- Tieren: It's a Gundam kit, yeah, but it's really not like most other Gundam kits. It looks much more like "hardware" than other Gundam designs do.
- Loto: Another Gundam kit - it transforms into a tank...
- Frame Arms Gourai: Kind of similar to the Loto, actually...