Beneath a Steel Sky and Flight of the Amazon Queen are available for free from scummvm.org. Other games are available cheaply from online retro gaming shops or perhaps somewhere like eBay, or you probably have a few old CDs somewhere in that box in your attic.
To install a ScummVM game on Android you need 3 things:
The ScummVM wiki pages are really helpful here. If you search for the game in question, you should find a page describing the game, the engine it requires and any other special instructions or limitations. The "datafiles" page also lists the minimum set of files you need to copy for each game, if you want to conserve SD card space. If you are choosing audio compression codecs (eg: for CD audio tracks), note that the ScummVM Android port supports ogg and mp3 (ogg preferred), but not flac.
Let me know if you get stuck (my email address is in the market details for ScummVM apps). Be sure to let me know what you tried and where exactly things went wrong, since "it didn't work" isn't enough information for me to help you ;)
If you can't find the ScummVM core app on the market, then you are looking from an Android 2.0+ device (Droid, Milestone, Nexus1, etc). ScummVM doesn't support these Android versions yet (but will).
If you start ScummVM and see an immediate crash, or a crash immediately after the unpacking progress bar reaches 100% then ScummVM doesn't work for you yet, sorry. I know about recent cyanogenmod versions and Android 2.0+ (Droid, Milestone, Nexus1) - anything else, send me an "adb logcat" covering app start until crashdump.
If you think you have done everything correctly, but ScummVM still can't find your game, you should check that ScummVM has found your plugin correctly. From the ScummVM launcher, hit "About" and look for the "Available engines" section that scrolls past. If that does not list the plugins you actually have installed, then you may be hitting one of two known bugs:
In general, ScummVM error messages are sent to the Android logs, so looking at them will likely be the first step in troubleshooting any new problems. This involves installing the Android SDK, enabling debugging over USB and running "adb logcat".
The original games and ScummVM were originally written for a PC or near equivalent. Keep this in mind when using the port and please be a little forgiving of some of the UI awkwardness.
All the game engines that are enabled by default as well as MIDI emulation and support for OGG and MP3 compressed audio. Note that there is no FLAC support. See the "About" dialog in ScummVM for specific information.
How did you do this? Is it Java?
No. ScummVM is a C++ program. For this port, I turned it into a really big JNI library so Android still thinks it's running a Java program, but almost all of it is implemented in C++.
This is why you can't find ScummVM on the market from an Android 2.0 device.
Correct. Until you've upgraded to Android 1.5, you want to stay on the previous version of ScummVM. If you've mistakenly upgraded you can find the old version here. I could put lots of effort into compatibility layers instead of fixing other issues in ScummVM, but realistically Android 1.1 and older is no longer supported.
This one is a surprise - it should work. Symptoms are that the ScummVM launcher starts up just fine, but it can't find any of the installed plugins (ScummVM "About" -> "Available engines" is empty, for example). See this thread for the debugging so far.
If you can test the market ScummVM version (the one with separate plugins) on earlier versions of cyanogenmod to see if/when the problem first starts appearing that would be extremely helpful.
Update: more recent versions of cyanogenmod have diverged enough that ScummVM just crashes immediately instead. I expect the Android 2.0 compatibility changes (still in progress) will fix it for cyanogenmod users too.
This bug is my fault. To recover from the blank screen, you can leave the blank screen for a few minutes and Android will prompt you to kill the unresponsive ScummVM. Alternatively you can kill ScummVM by finding ScummVM in Settings -> Applications -> Manage Applications, and hitting "Force stop".
This almost always means that the native code is failing to load for some reason (Android doesn't seem to let me catch the exception and show a more useful error message). You can see errors and stacktraces in the logs via adb logcat if you want proof.
If you have a new phone, then there might not be a version that will work for you yet. If you have an older phone (or rather, an older Android OS version) then you can try various previous package builds listed here.