How is meditation considered a good deed? I have heard it said that meditation is "the greatest good deed". Is this considered to be true in Buddhism? If so, how is meditation superior to all other good deeds? It seems self serving compared to other good deeds, such as generosity.
Because generosity alone can only get you so far. One's hindrances, defilements, ignorance, etc. are still there. Meditation and moral virtues are required to get one further on the Path. Matter of fact, through meditation, one becomes a more virtuous person and that itself is a superior kind of generosity. As taught by the Buddha in AN 8.39:

“Here, a noble disciple, having abandoned the destruction of life, abstains from the destruction of life. By abstaining from the destruction of life, the noble disciple gives to an immeasurable number of beings freedom from fear, enmity, and affliction. He himself in turn enjoys immeasurable freedom from fear, enmity, and affliction. This is the first gift, a great gift, primal, of long standing, traditional, ancient, unadulterated and never before adulterated, which is not being adulterated and will not be adulterated, not repudiated by wise ascetics and brahmins. This is the fourth stream of merit … that leads to what is wished for, desired, and agreeable, to one’s welfare and happiness.&quot;
“Again, a noble disciple, having abandoned the taking of what is not given, abstains from taking what is not given … abstains from sexual misconduct … abstains from false speech … abstains from liquor, wine, and intoxicants, the basis for heedlessness. By abstaining from liquor, wine, and intoxicants, the basis for heedlessness, the noble disciple gives to an immeasurable number of beings freedom from fear, enmity, and affliction. He himself in turn enjoys immeasurable freedom from fear, enmity, and affliction. This is the fifth gift, a great gift, primal, of long standing, traditional, ancient, unadulterated and never before adulterated, which is not being adulterated and will not be adulterated, not repudiated by wise ascetics and brahmins. This is the eighth stream of merit … that leads to what is wished for, desired, and agreeable, to one’s welfare and happiness.&quot;