Amazon recently introduced a Free Usage Tier for its Web Services. Basically, you can try Amazon EC2, with a free micro-instance (specifically, enough hours to run such an instance full-time, and have a few hours left over to run a second instance, too; or you can presumably use a bunch of micro-instances part-time), and the storage and bandwidth to go with it.

Here’s what the deal is worth at current pricing, per-month:

• Linux micro-instance – $15
• Elastic load balancing – $18.87
• EBS – $1.27
• Bandwidth – $3.60

That’s $38.74 all in all, or $464.88 over the course of the one-year free period — not too shabby. Realistically, you don’t need the load-balancing if you’re running a single instance, so that’s really $19.87/month, $238.44/year. It also proves to be an interesting illustration of how much the little incremental pennies on Amazon can really add up.

It’s a clever and bold promotion, making it cost nothing to trial Amazon, and potentially punching Rackspace’s lowest-end Cloud Servers business in the nose. A single instance of that type is enough to run a server to play around with if you’re a hobbyist, or you’re a garage developer building an app or website. It’s this last type of customer that’s really coveted, because all cloud providers hope that whatever he’s building will become wildly popular, causing him to eventually grow to consume bucketloads of resources. Lose that garage guy, the thinking goes, and you might not be able to capture him later. (Although Rackspace’s problem at the moment is that their cloud can’t compete against Amazon’s capabilities once customers really need to get to scale.)

While most of the cloud IaaS providers are actually offering free trials to most customers they’re in discussions with, there’s still a lot to be said about just being able to sign up online and use something (although you still have to give a valid credit card number).