favorite/most useful verb tenses?

[haka]

I used to always say that I MUST DO things in japanese just because i liked the way that-なければならない sounds.

いかなければならないんです。 i must go.
　食べなければなりません。 I must eat
　この地下鉄を乗らなければなりません。 i must take this train

Does anyone else have favorite verb patterns/sentence structures

いかなきゃ！