What is the best chain tensioning method?

[lclements]

Thanks everyone, I ended up buying one from the seller posted earlier, but I went for the one with an alloy cog: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=370310180721&ssPageName=STRK:MEWNX:IT

I also bought a SS spacer kit as I've been cheaping out by using plastic cassette spacers which flex quite a bit

Thanks for all your advice