now I've seen everything

Now I've seen everything AND Now I've seen it all — (Ну ни фига себе)— теперь меня больше ничем не удивишь.

Used for saying that you find something very shocking or surprising.

Example: A child divorcing his parents? Now I’ve seen it all!

Other ways of saying that you are surprised or shocked

Funnily enough (used for saying that you think something is surprising or unusual)

You don’t say (used for saying that you are surprised by what someone has told you)

Heavens above (used for showing that you are very surprised)

Well, I never (did) (used for saying that you are very surprised)

Is that a fact? (used for answering someone when they have told you something that you consider surprising or unlikely to happen)

You would not believe (used when you are going to tell someone about something unusual or surprising)

[Of all things] / people / places (used for expressing surprise that a particular thing / person / place is the one involved in something) — ни больше, ни меньше; подумать только!; ну надо же!

see also
[Who would have thought...?]
[Who da thunk it?]
[ну ни фига себе]