They work best in stouts and porters for my tastes. Chilli and chocolate is a great combination. Depends what chilli's you've got and what they offer in flavour and heat. Durham Brewery occasionally do Hellfire, an imperial stout with Naga that's great but full on. My local brewery, Redwillow, use deseeded Chipotles to make Smokeless, a porter that has very little heat, but a lovely smokey flavour.