인사 (Greetings)

Perhaps what we all know is only Annyeong Haseyo and Thank you, i.e. 감사합니다 (gam sa ham ni da) or "gomab sumnida"

Here is a list of additional greetings in Korean.
Your welcome! /Don’t mention it!
아니에요. (a ni yeh yo)

It’s Ok
괜찮아요.(goaen cha nah yo)

I am sorry.
미안합니다. (mi an ham ni da).

Good night! / Sweet dreams!
Adult & Elderly
안녕히 주무세요. (an nyeong hi ju mu seh yo)
The answer is the same.

Friends & Kids
잘 자.(jal ja)
The answer is 너도 잘 자 (neo do jal ja)

Nice to meet you.
만나서 반갑습니다. (man na seo ban gap seum ni da)

Nice to meet you, too.
네, 반갑습니다. (ne, ban gap seum ni da)

Have a nice weekend.
주말 잘 보내세요. (ju mal jal bo nae seh yo)

Thanks, have a nice weekend, too.
네, 주말 잘 보내세요. (ne, ju mal jal bo ne seh yo)

Source: Kozine Magazine, January 2009