Right, seeing as it gets asked alot. For E36 328i's without an LSD (or those with that need it replaced), this is the part you need:
33141209655 - LSD Assembly (the clutch bit, inside your diff housing).
The price is £470 plus VAT from BMW, delivery in 3-5 working days. If you've got an old LSD unit to exchange, they'll knock 80 off... woo hoo!