For riders in the UK, Exol Optima Racing 2 Stroke oil.
http://www.exol-lubricants.com/automotive/products/details/?PID=62
This all looks too good to be true - a high spec racing oil for around ?5 per litre! If you buy bulk containers of 20 or 25 litres it works out as cheap as ?3.50. Check out eBay listings or Lubetech in Leicester. It is a red oil with a low flashpoint, very similar to Castrol TTS.
Don't be concerned by this, it's an incredible oil that performs at least as well as the brand leaders costing 2-3 times more. Very clean burning, minimal smoke and spooge and the engine is always very clean inside. Any carbon deposits are easily wiped off.
Very well known inside the UK KTM riders forum and used by most riders on there. I have been using it for several years and wouldn't buy anything else. Runs fine at 50:1. UK made too.
Probably just proves that the main brands are a ripoff.