The basic hierarchy of clever, CNC cutting goes:

Water Jet (best)
Laser
Plasma

There's no point having unnecessary cost or precision and for general fabrication plasma is pretty good. Helps that I've been using the same company (Phillips Engineering in Suffolk) for so long now that I've moved on from father to the son who now runs the company.

Hi R
I am a big fan of water jet cutting and have a super supplier here.
They can cut to a 10th of a thou.
It is superior to laser cutting and you can cut very diverse materials.
If you send me a sample or drawing I will get you a quote.

Location: The Centre of the Universe

Charles is right, depends on the quality you require. Although at the top of that list I would add CNC machining if it has to be absolutely perfect!

At work we use CNC machines (including a 5 axis and a giant industrial robot arm that used to weld cars that mainly gets used now to cut polystyrene!) for detail stuff. We have a plasma table for rough stuff (not a great one, generally needs a lot of clean up) and lasers but they are small so those are only for plastics and wood. For tiny detail things the lasers are great and are very accurate depending on the material. We send bigger stuff out for water jet cutting if it needs to be accurate and clean.

I'd say work out the exact precision you need then see if the suppliers can do it. I know they've looked at getting a water jet cutter at work and the maintenance/running costs were horrendous so you probably want a place that looks after their equipment well to get the best results.

Simon

Location: Wellington

All your advice and offers here, and through email, are very much appreciated - thank you very much indeed.