I've got the Martindale HPAT600 Hand held pat tester.
Don't make the mistake i did, and buy something expensive if you're not going to be using it often.
Got it 18months ago and it's still nowhere near paying for itself.
I don't ever encourage buying cheap and cheerful (you buy once, you buy twice ect..) but it's PAT testing we're talking about here so the cheaper the better.