Surprisingly enough you can actually do command-line tagging using foobar2000. For what you want to do you will need to make sure you have id3v2 support installed: I think that if you run the Special installer there is an option to include this but if not then you need Kode54's foo_id3v2 component. You also need to set it to write id3v2 tags by default by clicking on Preferences -> Playback -> Input -> Standard inputs and setting "Tag type to write" to either "ID3v2" or "ID3v2 and ID3v1", whichever suits your needs.
Please take note that it will strip other tag types from the file. So if you want ID3v2 tags and will also have mp3gained the files (which writes APEv2 tags) then it will strip the mp3gain tags. So this method will only work if you are happy to have only ID3 tags, or to add any other tags at a later stage.
Once this is all set up you can then tag from the command line, for example:
CODE
foobar2000.exe /tag:Title="My Song";Artist=Me;Genre="Acid Jazz" "test.mp3"
One side effect of running this command line is that as well as tagging the file it will also launch the foobar2000 GUI. However, if you open the GUI before you start and minimise it you can then tag from the command line as many times as you wish and the GUI will stay hidden.