I was surprised by a pair of Presidian PBS 5053 bookshelves I grabbed at RS back in the mid 00's on close-out sale of $19 (IIRC). With a decent amp, and some sponge foam on the back internal wall, these really sound good and go lower than their specs list. With a bass-heavy Realistic STA 2280, the bass response is extremely smooth and sound like a 10" woofer should sound like despite being 6.5"
Alpine Type R 10" subwoofers in a tuned, internally baffled and rectangular ported boxes are the best sounding subs I've ever come across. I spent years wasting money on JL Audio W3, W6, Crossfire BMF, etc. and on a whim, I grabbed a 10" Alpine R and even went with a store made box and run it at 100w up to 450w and still fails to please. It's still as tight as it was a week after I bought it. Hard to believe a $200 sub can outpace a $400-600 sub with actual sound quality. I don't listen loud anymore, but when I want it, it's there. It also sounds really good at lower listening levels where it spends 98% of the time. Used it for a home theater set up initially at 100w and it was great for that purpose too.
MCS 3233. Despite it's 33 wpc @8ohm, it sounded more like a punchy 80 wpc after putting slightly higher rated fuses in and exhaust fans on it so it'd run cooler (It's possible I might have been running it at 4 to 6 ohms, hence the original fuses popping at higher volume, so it might have been doing closer to 50 wpc and the fan kept it alive longer than possible). Had a high THD, but man it rocked. Was once told by my buddy's dad that he thought it was closer to 100 wpc given how loud it could get w/o clipping, and he had higher-end stuff so I always took that as a compliment, but I remember he was the one that taught me about THD and showed me the difference with "noise" inherent to the amps between that one and his, which had none LOL.