I'd like to see a manufacturer make a seriously fast car that runs on an alternative fuel.

Bio-ethanol, or alcohol, or chip fat, whatever.
And in regards to the hp-wars, yes, it does get tedious. I'm quite over the bigger, faster, more thing. The biggest gripe I have against the constant stream of new and bigger engines is weight. Cars are already getting heavier by the day with all the luxury and safety gadgets in there, last thing we need is another 100 kg's extra by using V8s instead of I6's (random example).
It's like these days car manufacturers only look at the spec sheet and that's it. It always has to have more than the other guys, while because everyone thinks like that, no one is actually going to be the fastest by a good bit. I mean, new M3 went from inline to V8, new Skyline's/Supra's are going to have upscaled engines, all AMG's are switching to the 63, ditching the 55. The only really suited cars I can think of for continually bigger engines are, indeed, the big luxury saloon puddings, because those things weigh as much as Siciliy already. An S-class won't have it's handling characteristics upset because of 80 more kilo's in the engine bay, since it handled like a fat kid on rollerskates in the first place. Same goes for Audi 8's, BMW 7's, etc etc. Even with the new S8, it's a sort of weird mix and in the end up you're stuck with a car that misses it's point. I mean, the basic 8 is a big luxury saloon. Add a huge engine and it becomes a sports saloon or whatever the marketing trolls tell you. Well, go the performance nutters, it needs to handle too! So Audi complies, sets the car up so that, for a two tonnes barge, it handles reasonably well for a car it's size and weight. But then you're left with a huge luxury saloon with an even bigger engine and massive straight line speed and a ride that's awful.
It's like building a Lotus Elise that's exquisitely comfortable on 40mph B-roads. It defeats the purpose of the car. I mean, honestly, who here really wants to take a car like an S8 or a S65 to play on a madly twisty road? I don't. Those things are made to woft you along the Autobahn on a saturday night 3 am at a measly 280 km/h. They're not made to be thrown around on a small road.
So that's my biggest gripe. Pointless cars and pointless versions of otherwise excellent cars.
Don't get me wrong, I like the idea of more power. It's just that I dislike the idea of the focus laying purely on more power. I want more general package instead of an engine spec list worth 20 minutes guaranteed bragging rights in the pub. And shed weight. Weight kills. And anyway, in the end, no one is buying car B because it happens to have 535 bhp instead of car A's 510 bhp. When you are really a contender for buying seriously fast cars, other factors will determine. Looks, road behaviour, ride quality, interior, etc etc. The 30 more mustangs than the competition isn't going to save you if the car is crap anyway.