I'm not going to say anything, I'd rather my favorite parts didn't get any more expensive!
I flipped a bike with those challenge derailleurs. You're right; they work great.
I'll try to think of others...
Deore DX - it looks great, it's durable and you can find it inexpensively on parts bikes.
Most underrated components?
● 1971 Grandis SL ● 1972 Lambert Grand Prix frankenbike ● 1972 Raleigh Super Course fixie ● 1972 Peugeot UE-18 Mixte ● 1982 Motobecane Jubile Sport ● 1983 Nishiki Landau ● 1984 Peugeot PH10LE ● 1984 Bianchi Limited ● 1985 Peugeot Vagabond ● 1985 Trek 600 ● 1985 Shogun Prairie Breaker ● 1985 Raleigh Elkhorn ● 1986 Univega Nuovo Sport ● 1987 Schwinn Tempo ● 1996 Kona Lava Dome ● And a Bike to Be Named Later ●
Another vote for Deore DX 95% of XT, 25% of the price.
The mid-1980 Shimano Z-series. Reasonably priced, nicely finished, works very well, bullet proof.
Old Falcon branded triple front derailleurs. Work fantastic, and you could probably get them at 10 for a buck.
"Where you come from is gone;
where you are headed weren't never there;
and where you are ain't no good unless you can get away from it."
I'd vote for Araya steel rims, if you can find a perfect set.
I believe that these are the smoothest I've ever used in terms of braking, and not too terribly heavy.
Not the MOST underrated, but I have a fetish for Lyotard pedals. They're not smooth, but they are quite durable. There's only one model I know of with a design flaw. It has an aluminum shaft around the spindle. But I don't have that model. I'm hoarding all the Lyotard rat trap pedals I can find. I don't even know why.
I'm finding that a lot of the stuff I like is well regarded and priced accordingly.
*Recipient of the 2006 Time Magazine "Man Of The Year" Award*
Anything tubular and freewheel in the same wheel. Hubs are worth 95% of the whole wheel if they are C-Record , Mavic 501, almost any freewheel wheelset for that matter. Specialized Flag CS's, last generation of Tricolor single pivot brakes , great performance from a single pivot with the tricolor levers. Suntour XC comp brakes and CS's. Winner branded hubs.
Simplex Prestige derailleurs. Perform well for me. Victim of cycling myth.
Shimano 1050 6-sp indexed. Light, capable, cheap, and polished.
I'm not a doctor, but I watch them on TV.
1982 Lotus Classique
1987 D'Arienzo (Basso) SLX
1995 Hot Tubes TT
2006 Cinelli XLR8R-2
2008 BMC Roadracer SL01
2014 Wraith Hustle
2014 Wraith Paycheck
Mavic 500's are underrated but have a following. I thought they would be easy to find because they are not mentioned that much. Boy howdie did I get a surprize when I did find them. Typically they are priced the same as Campy HF hubs or more. Try to find skewers! Ha!
French bikes because of their non standard dimensions.
Suntour XCD - I have a couple 6000 rear derailleurs and they have been flawless for me.
1975 Motobecane Le Champion
1984 Bridgestone 400 -- 1985 Specialized Expedition 1986 Cannondale ST400 and Nishiki Cascade -- 1987 Trek Elance 400T and Schwinn Voyageur
1990 Cannondale ST400 -- 1994 Univega Via Carisma
For C&V, old Weinmann brake levers - cheeeeeeap prices, lightweight and they work. Comical of the market value difference vs. old Mafac (and those crazy prices for Mafac hoods...whew!).