Those of you interested in studying Aspect might be interested in a brand new volume from Cambridge:
The Development of English Aspectual Systems: Aspectualizers and Post-verbal Particles (Cambridge Studies in Linguistics) by Laurel J. Brinton
Getting an idea of how Aspect works in your own language might help in understanding it in other languages. The biggest hurtle is always comprehending the concept more generally.
With that said, I don’t know if I’d recommend a book from this rather technical series to start out on. Perhaps this one is going to be of interest more to those of you who are simply interested in Aspect or interested in English.