The current trend to use the Meditations as a self-help manual of sorts isn't entirely misguided, but it is incomplete. Marcus Aurelius' (121-180) single surviving work was the result of a life of reflection and action, the sort of life any practical philosopher should have. Roman emperor, general, scholar—there were few spheres to which he wasn't committed, most of them simultaneously. His notes on living the good life, remaining undaunted by good or bad fortune, death and love and fear are as relevant and cogent today as they were almost two thousand years ago.
Aurelius, while not technically one of the Stoic philosophers, exemplifies Stoicism. (A Stoic isn't a grouchy person with no emotion; a Stoic values reason and judgment over emotionalism and seeks mastery of his inward self in order to pursue wisdom and nobility.) He describes catastrophe, violence and bliss with calm and a level of detachment most of us would be literally unable to foster. But far from making his observations unrelatable, his coolness increases his insightfulness and allows him to get at the truly human element of everything he observes. He may have transcended emotion (at least in his writing) but his perceptions are far from irrelevant.
This is one of the first spiritual memoirs. While it isn't "autobiographical" in the sense we usually mean, he documents many of his own experiences from which he draws universal principles, much in the way St. Augustine did 250 years later in his Confessions. Aurelius was not a Christian, but unlike most Roman emperors he wasn't particularly spiteful or suspicious of them. Many of his spiritual observations actually hold true as much for Christians as anyone else, like his frequent admonitions to avoid anxiety and let things take their course.
Far from a coherent narrative or even series of essays, the Meditations are episodic, aphoristic, brief. Aurelius' writing is sparse and strong, newly (and brilliantly) translated here by Gregory Hays. The first chapter, in which the author delineates his influences and progenitors, remains one of the most famous and most affecting in all of literature (and is strong proof that he never completely disengaged himself from emotion). Whether you want someone else's thoughts to ponder, or a jumping-off place for your own contemplation, you could hardly do better than this classic of philosophy and reflective memoir.