Wow, you people are amazing! I hadn't noticed how old the thread was, but I shall ask anyway:-
Two YA sci-fi stories from, I think, the 1980s. I don't even know if they were any good but they've stuck in my mind ever since, so they've clearly got something.
First is definitely a novel. It concerns some boys and a science teacher, who's generally considered a bit weird because he won't have any technology in his house. The drama develops into a terrifying bid to take over the world by some sort of satanic bank whose head office reaches from the ground to the stratosphere and is full of fire. The world takeover's implemented by making everyone have a bar code stamped on the palm of their hand or forehead (yes, blatant religious overtones!) The professor's ability to interpret barcodes somehow enables the boys to infiltrate the devilish bank and save the world.
The second, I thought, was a chapter in the Hitchhiker's Guide To The Galaxy - but am pretty sure it isn't! There's a gas planet, populated by enormous, whale-like creatures that live for millennia and have growths on their backs which develop into full landscapes over time. Other creatures have evolved to live in these floating countries. The whales are constantly attacked by horrid birds that take bites out of them. When a whale loses a critical mass through bird bites, it sinks through the planet's atmosphere and all the creatures living on it die. There was a funny scene where two of the floating whales have sex.
Ringing bells for anyone?