Jaabir Ibn 'Adbullaah (radhi-yAllaahu 'anhu) related that the Messenger of Allaah (sal-Allaahu 'alayhe wa sallam) said: Verily, the best supplication is:
الْحَمْدُ لِلَّهِ
All praise is for Allaah.
Alhamdu lillaah.
...and indeed, the best form of remembrance is:
لاَ إِلَهَ إِلاَّ اللَّهُ
None has the right to be worshipped except Allaah.
Laa'ilaaha'illallaah.
At-Tirmizi 5/462, Ibn Majah 2/1249, Al-Hakim