The MEME Suite is a free-access collection of tools for motif discovery and search, developed by the University of Queensland and the University of Washington. MEME stands for "Multiple EM for Motif Elicitation", where in turn "EM" stands for the expectation–maximization algorithm.
One of the key tools of this suite is also called "MEME" and is intended for discovering motifs in a given group of sequences. MEME calculates all common motifs above a statistical confidence threshold and outputs them in the form of a sequence logo. This tool can be directly accessed here.