I've been very impressed by the online archive of classical texts at theoi.com, and have been using it to verify dubious-sounding claims from e.g. Robert Graves against the text of the myths themselves.
However, sometimes, theoi will cite a "scholiast" as a source for its information - for example "Schol. ad Theocrit" (Scholiast of Theocritus). Printed references, like Smith's "Dictionary of Greek and Roman Biography and Mythology" also sometimes cite these. And while the text of the myths is hosted on theoi to check against, I cannot find the scholia anywhere, either on that site or on the wider Internet!
This is mostly a request for information on where to find English translations of the scholia. But if these translations generally don't exist - if the scholars tend to work from the original Greek and Latin texts of these, for example - then please let me know. I really don't want to spend too long fruitlessly searching for e.g. "Schol. ad Apollon. Rhod" (which AFAICT is actually a scholiast on his Argonautica!)