Without irony, you can use

effectivement

or

en effet

It seems to me that the first one denotes a little higher language level, and is used more rarely in casual conversations. But this highly depends on the tone.

A modified version, close in pronunciation, is written:

anéfé

and is being used too, from the gimmick of a caricature of famous persons in TV shows (see here for instance).

Other options could be possible, like

Carrément !

or

Tu m’étonnes

C’est clair

Similar expressions in English include:

I’d say

You bet

Too right

Tell me about it

Do not forget the space before the
! sign in French.

If you use it with some irony or doubt, you could say:

Vraiment ?

Eh bien !

“Indeed” is quite formal in English so to keep the same tone, a good translation would be:

• En effet !

In casual spoken French, you are more likely to hear:

• Oui !
• C’est vrai !
• Absolument !

and other similar replies, including even:

• Tout à fait, Thierry !