Spam-prevention API?

Are any of you integrating with a spam-blocker API/service you like? (e.g., Akismet, Mollom)

A significant feature of my product accepts form submissions on behalf of my customers. Because the typical form lifespan is only 2-3 months, spam hasn’t been an issue but I’m sure it will be eventually.

I hate captcha with the fire of a thousand suns, so I’d like to integrate with a service API that does intelligent analysis of the user input, and blocks at least most spammy submissions. Form fields will vary quite a bit from customer to customer, so it needs to allow for flexible form structure.

I’m planning to pay for it, since it’s something I don’t have to build and it provides significant value.

Can’t go wrong with Askimet. Although it’s been a few years since I integrated it.

Thanks - their API looks straightforward, and their pricing is super reasonable ($5/mo at my level) Akismet sounds like a perfect place to start.