To clarify this matter further. It's not enough to say "with regard to" is standard usage. The question is why?
Answer:
- When people say "with regards to" they are confused about whether "regard(s)" is a noun or a verb. In fact, in this case "regard" is a noun.
- "with regard to" is like "with reference to". You wouldn't say "with references to".
- "reference" and "regard" are both nouns, coming after a preposition, "with".
- As the earlier reply said, "in regard to" is also correct. And "as regards" is fine too, "regards" being a verb in this case.