Class 6 is minimum recomended for installing NITDroid without issues (i assume the same for other OS). About microSD it doesnt really care about brands, manufacturers or whatever. Buy the cheapest you can for this specs (avoid Sandisk, has issues with NITDroid).
I already order an 8Gb class 10 microSD for more or less the same ammount in amazon.co.uk. Check it out, also eBay and so.