I know his name has been mentioned in passing on a couple of occasions in this forum, but I think Castro deserves a topic of his own on the strength of his piano concerto alone! I refer those interested to a performance on youtube, and although presented in rather disjointed chunks! - gives a more than adequate overview of the work and should hopefully start up interest (I know Mike Spring has seen the score and initially thought it rather weak - but I beg to differ and I am sure there are others that would too!)
http://www.youtube.com/watch?v=DQH8ZmaYHcc
Then of course there is his piano music, a fair amount of which has appeared on a variety of Mexican labels that seem to be extremely difficult/well nigh impossible to obtain. (Can anyone tell me where I can obtain Quindecim recordings - they seem to have a fair catalogue including much 19th -early 20th century Mexican classical music - one of their CD's is a complete recording of Castro's valses pour piano?) There are a few odd pieces on IMSLP for those interested, but there also seems to be (if only one can know how to obtain them) a number of fairly recent published scores, including a volume of waltes. Castro studied in Paris with, amongst others, Moszkowski.
I also thoroughly recommend the cello concerto for those who like their late romantic concertos, and this one doesn't disappoint, although the performance is not top rate (once again, perhaps Hyperion's Cello Concerto series could be kick-started with this one!). There is also a rather poor recording of his first symphony, which is probably the least interesting work I've heard to date, and certainly seems to be more of a student exercise.
However, the piano concerto is surely a must!