Also, the Buffalo belay jackets are another - slightly different possibility. I used the original one for years with the full Buffalo system.
Having, say, a down jacket without a hood or with a detachable hood is still a hell of a lot better than nothing when your mate takes two hours to dig up the crux in a Cairngorm mid-winter maelstrom, so don't despair if that is what you already have, or if all you can afford is a (very reasonably priced) Alpkit Filo - just 'man up' and try to have fun! But if you are thinking of specifically buying a belay jacket, or are in the market for your first insulated jacket for climbing of any type - hopefully the thoughts above will help you sort through the contenders. I'd say see you up there, but you won't because I'll be the one hiding in the hood of the big DAS Parka.