There are already a load of places people can download or access your Android applications, other than the official Market. If you're a developer, you'll naturally want to explore as many places to sell and list your app as possible.
Some of the sites and applications describing themselves as marketplaces simply link into the Android Market, but on some of them you can upload and sell your apps directly. In this article I'll run through some of the main Android application stores I've found, focusing on those sites where you can distribute Android software, i.e. upload your Android APK files and sell them.
On the directories, you can sometimes sign up for an account and alter the details listed for your apps. Here are some I've come across, I haven't tried them all so can't guarantee they're any good. Also, some of these are new services and are just starting out, so they don't always have much of a user base yet.
Make sure you check out the terms, FAQs etc on any service before taking the time to sign up, many of them have high minimum payouts and restrictions on where developers can be resident etc.
AndroidZoom is an interface to the Android Market. As a developer you can link your app listings to your Google account, insert additional information about your apps and access additional data, just click the "I'm the developer" link on any of your app listings.
AndAppStore is a an Android app store aimed at catering to a wider variety of users than the mainstream market. As a user you need to install the app to access your downloads but can shop for them on a computer if you like.
SlideME is a community based marketplace for Android apps.
AndroidPIT combines an app store with articles and news etc about Android.
AndSpot is a new social networking based app store offering increased exposure and data.
ApplsLib is an alternative marketplace for tablets running Android. To use the service as a customer you need to install the AppsLib application.
Handango is a major app store for platforms including Android, Blackberry, Windows Mobile, Symbian and Palm.
Appoke uses social networking to aid app sales.
MobiHand is an app store for Android, Blackberry, iPhone, Symbian, Windows Mobile and Palm.
GetJar is an app store for many different handsets and platforms.
AppStoreHQ covers Android, iPhone and iPad, linking to the Android market for downloads and sales. You can claim your profile.
Androlicious is an interface for browsing the Android market, and you can link your apps to your Google account. You can submit apps and information to them via email.
AndroLib is another listings site, but they have quite a lot of informative statistics and charts on the app pages. You can claim your apps by clicking the "I am the developer" link on the listings page.
So that's it for now. There are also loads of app review sites, but that'll be for another post... If you know of any good Android market store sites please do add them in the comments.
Update October 2011
In the short time since I wrote this post a load more marketplaces have started up and I have to admit I've totally lost track of them! One resource that may be useful for some developers is appbackr which I've just heard about so know very little about. It provides an alternative way of funding your apps and handles the distribution side of things for you. If anyone has experience using the service please do comment on how well (or not) it's worked for you.