[Coda]

There's "watakushi" which is EXTREMELY formal -- this is what you use when you say "I, <insert name here>, do solemnly swear" kind of statements. Gender-neutral.

There's "washi" that's getting rather old-fashioned (the stereotype is that only elderly men use it).

There's "ware" which is almost as formal as "watakushi" and largely a matter of literary style although you'll occasionally come across someone who uses it in speech. Technically available to either gender, but more common in men when it comes to media (as the level of formality it would imply tends to result in "watakushi" among shrine-maiden-type women).

There's "waga" and its derivatives that are very old-fashioned; these days they're only used when making big speeches.

There's "atai" which is further contracted from "atashi", and therefore even more informal. Typically feminine.

There's a whole slew of various dialectical slang that I won't enumerate, as well as a ton of archaically old-fashioned ones that are pretty much exclusive to period-style literature in current use.