This item is what I'm using now... it works fine - powered by 5V, outputs a logic high that my PIC can interrupt on, just a little "bare-bones"... doesn't look pleasant. Should either spend time putting it into some plastic case or buy something better looking - like the unsuitable Brennenstuhl I linked to in my first thread entry. I certainly don't mind paying an amount like £20 to £30 for something that would aesthetically do the business and work.
Also, these commercial (in the sense that they're being sold to the public, I mean) PIRs often have a light sensor included - so they only activate when a) something is sensed and b) there is a certain level of light.
My project does this, but I use a TSL237 as well... maybe there's a way I could get a PIR that would give me the logic high when both conditions are met?