My point was that you could set up shortcuts or whatever for each application that would act as keywords. So for the YouTube downloader you mentioned, you could set up "youtube", "flash", and "video" as aliases. This falls down somewhat if you have multiple apps that could use the same keywords. Like you probably couldn't use "download", since that would probably make more sense to be attached to an FTP client or something. But maybe there's one that supports the concept of tags.

I have no idea if Launchy is portable or not, but I bet that there's one that is.