I'm doing pretty well with RTK and this site, but I find that when I'm out in the city I look at kanji which I know I know from RTK, but I get the meanings confused. I know Heisig doesn't recommend it, but is there a reverse version of this site, i.e., from kanji to keywords? Or a similar program?

Anki could do that (google it or search the forums)

There's a Kanji to Keyword Greasemonkey script for Firefox. Plus there are a few threads on this topic, like this one.

Ah good point about Anki. I'm using it already so I'm sure I can find a Heisig kanji pack for it. Cheers