As previously reported, users of jailbroken phones and the developers who cater to them now have an avenue for commerce in apps: the Cydia Store. Smoking Apples visits the store and has a solid rundown, noting that Amazon Payments is the only funding source for the moment (PayPal is on the way, says Cydia lead Saurik/Jay Freeman). Users who update to the latest version of Cydia on their phones get the store capability automatically; if your phone isn't already jailbroken, though, you'll have to jailbreak it and install Cydia.
The limited number of apps on the store versus the overwhelming bounty of the official App Store may help users find the apps they truly want, says SA. Freeman has a list of apps queued up for release over the next few weeks before he begins accepting unsolicited submissions.
If the functionality you want and need is uncertain or unlikely to show up in the App Store (*ahem* -- tethering, anyone?), would you jailbreak your phone and buy from the Cydia Store?