Is your issue that they aren't available or that you can't tell which one is good?

There are far, far too many, and 95% of them are not very good. Even if you wanted to evaluate them all to try them out, this is actually quite hard - my searches start returning a mix of completely unrelated apps and relevant apps after a small number of results.

Don't know what your specific needs are, but I did a quick search and came up with London Transport Live (http://www.androidzoom.com/android_applications/transportati...), which from a quick play seems to do what I'd expect a transport app to do.

I know that the specific app isn't your point - it's more about the general question of discoverability, but I rarely find too much difficulty finding at least one reasonable example of the kind of app I'm searchig for.

The problem is, I believe, TFL won't open up their API without charging for it.

you may want to try http://tripease.info/en/

disclaimer: i know these guys