For example: in a conversation about food, when your friend says that the food is おいしい, then you can also say おいしいね, or そうだね.
Are there other ways you can say in agreement? Perhaps a phrase similar to 'I Agree!' or 'Yes! Really!'?
Totally overkill (and maybe that's what you're going for) but 賛成!works pretty much like 同感。Another one I used to love to do (which in the case of food goes really well with the over-acting one finds on Japanese TV is to do) 正解!(Correct!) like they'd say on Who Wants to Be a Millionaire.
The answers in your original post are arguably the most colloquial though. I will add that you need a certain level of fluency for this to not sound mechanic and weird. IMHO, anyway.
There is the word 同感 which basically means "feeling the same". It can be used to in the same way as "ditto" in English.
A: そのラーメン凄く美味しいよね。
B: (私は、) 同感だ。A: Those ramen are so much great.
B: I agree./ Ditto. / B just nods.
That said, there is not a lot of emotions packed in this (= 同感) expression. It merely expresses that you feel the same; just like "ditto" would.
For more colorful expressions, the comment from Choco describes some possible answers (more specifically related to Kansai). But you can freely use something like:
でしょう(ね)(isn't it ? / you're right !)
to express agreement with a previously said おいしい・うまい, regardless of dialects.