Hi Mick,
I like my Arkel panniers. They're designed very intelligently, they're extremely tough. It's easy to get the bags on and off the rack, but the mounting system is rock solid. I think they're the best panniers around.
Arkel panniers are pricey, and they're water resistant rather than waterproof. They are highly resistant to rain, I should add, but in heavy rain you ought to use pannier covers and possibly plastic bags inside. Ortleib panniers, by contrast, are truly waterproof, and many people prefer them for that reason.
There are other brands people use here, and they seem to do pretty well.
Arkel:
www.panniers.com