There are two or three tools / techniques which have transformed my cooking.
   Here they are:



All your sauces become light and creamy. It is well explained on the bamix site, and Gordon Ramsey loves it.

Sous vide cooking

A real revolution! Your meat and fish are perfectly cooked, exactly how you want them. You put your meat or fish (or vegetables) in a special bag, apply the vacuum, and then put them in the "sous vide" water oven, at exactly the temperature you want.
No more overcooked fish or undercooked meat!
Slow cooking possible as well. Everything changes!
The cheapest is to buy it on internet (brand SousVide supreme), but check out other sites where it can be cheaper .
You also need a Vaccum Sealer, and the bags
For more info see, for example Heston Blumenthal at Home and Thomas Keller Under pressure: Cooking Sous Vide.


Electric thermometer

Not really a revolution, but it helps. But there is something you need to know. Do not believe those who say that everything will now be perfectly cooked (though this can be true for "sous vide"). The thermometer measures the temperature at just one point. However a roast, especially, will have different temperatures at different points. So the thermometer can give a false sense of security. Use it in conjunction with the good old fashioned methods you used before. And do not forget, the temperature at the centre of a roast will continue to increase, even when you take it out of the oven.