I pronounce it like Top Gear does.
Koenigsegg - Kown-en-zeg (technically Ko-en-ig-zeg, but you say it so fast, they run together)
Porche - Pour-sha
Gallardo - Guy-are-dough
Murcielago - "Mercy-el-ah-go" (another one where saying it fast it might sound different because it runs too fast.)
Bugatti - Depends. Sometimes "Bew-gaw-tee", sometimes "Bew-gat-tee".
Veyron - Sometimes I say "Vay" or "Veh", sometimes I say "ron" or "rin".
Audi - "Ow-dee"
Also, every now and then, I'll slip up and call Volkswagen by it's proper "Volks-vawg-en" pronunciation since it's such a fun accent to fake.
I also didn't know Countach was "Coon-tash" until yesterday.
And apparently, Top Gear says "Peugeot" like "Persio". Persia with an "O", but I'm still curious how it's pronounced.