As far as underrated= quality for price, I'd say Bersa. They're ALWAYS the budget option when you can't afford a better brand, but most people seem to like the ones they own. And as far as customer service, they once replaced my brother's 380. He kept it in his car under the seat, and that car had a fuel line leak and catch fire. The car burned
.
He took it to a shop, they sent it in, and he got a brand new one with no hassle.
I'd say the Filipino 1911's fit in that group. I've got both an Armscor and an ATI, they're nice guns. Not Ed Brown nice, but not a dang thing wrong with either, and we're talking a cheap, basic 1911 in .45 acp with lifetime warranties.
Under the radar, I'd say the Turkish brands, like Sarsmilaz, Canik, Tisas, Girsan etc. People look at them sometimes and get snobby on brand (or country of manufacture), but they're good guns at a very good price.
Along those lines, some of the other European manufacturers. Spain had a bad reputation mostly due to Ruby pistols and Llama's that weren't quite 1911-spec, and that unfairly affected Star and Astra. Those were top-notch guns, I have a few Stars and they're great.
Zastava, a Serbian company, sometimes gets laughed at as cheap. But some of those poking fun might have Zastava-manufactured guns that US brands just imported, such as rifles etc, and never realize how silly they look.
FEG in Hungary, another closed shop, also made nice guns. They sometimes got frowned on because of making unlicensed copies of stuff (Hi Powers, etc). But they were good to go. They made some stuff for Walther.
Somebody mentioned Daewoo... I have a DP 51 I got for cheap. It's great, they just didn't get a good import deal. It's funny that someone would call them crap, then look at a Lionheart, which is just a Daewoo with cerakote.