I guess my old Dell Inspiron laptop (an original 1100, from 2002) probably qualifies fairly well. Although she now runs multiple versions of Puppy Linux, she originally came with one of the first releases of XP Home - yes, we've had it all those years!
It weighs in at around 8 ½ lbs; the biggest part of which is accounted for by the massive, 20.4 volt, 17-cell Li-ion battery pack, which by itself probably weighs the best part of 5 lbs..... The weight is critical to the laptop's balance; without it, with the lid open, it's on the point of tipping over backwards! (This is due to the heavy metal frame around the LCD panel, inside the lid; everything on this baby is built like a brick outhouse.....unlike many modern machines, which will bend if you look at them wrong!)
The reason for that massive battery pack? This thing runs a full desktop Pentium 4 CPU, with that chip's normal power requirements.....a TDP around the 70W mark. Low-power, mobile processors were still just a gleam in an Intel engineer's eye when this was built.....
You can still find these around on eBay/Amazon, from time to time. Do be aware that the majority of them came with pretty small amounts of RAM; ours originally had all of 128 MB of the stuff. It's since been maxed out to 2 GB, the most the 845 chipset will support. She's also been treated to a 64GB KingSpec IDE-interface SSD, which has made a huge difference to boot times.
Look out for the Inspiron 5100, too; this was essentially the 1100's 'big brother', which came with a top-spec P4 and around 512 MB of RAM.....and built-in wireless. Ours originally came with a 2.2 GHz 'Celly'; the 2.6 GHz P4 was added by me, around 6 years ago; since it has no native wireless capabilities, I'm using a 'period' PCMCIA wireless card in the slot below the hard-drive caddy.
Still runs sweetly, if a little slowly by today's standards.....and remains productive, and useful with 'Puppy'.
Mike.