From my email, adapted from the NIV Quest Study Bible by Zondervan.
This unique Bible addresses the common, uncommon, and perplexing questions people ask about Scripture.
There are many ways to categorize the psalms. Some focus on content (trouble or trust, praise or prayer, joy or repentance). Others emphasize the use of the psalms (public ceremonies, private prayers and so on). Still others analyze style and technique (such as parallelism and acrostics). Here are some general categories:
(1) Hymns of praise. Many psalms were used in temple worship and some even include directions for the song leader. Many are still used as the basis for hymns and praise choruses.
(2) Complaints. Life is tough and many of the psalms reflect that fact. People turn to the psalms in times of distress because the psalms dare to be honest and meet them right where they are.
(3) Royal or Messianic. Many psalms revolved around the king and were intended to be used for public occasions in the life of the nation of Israel. Early Christian teachers, however, recognized that these psalms contained prophetic allusions to Jesus Christ, the King of kings.
(4) Occasional. Referred to as songs of ascent (Ps 120–134), these psalms were so named because they were sung by Israelite pilgrims as they went up to Jerusalem for the annual feasts. Other special occasions often had their own psalms as well.
(5) Wisdom. A few psalms illustrate the difference between human folly and godly wisdom, between sinful and righteous behavior.
Other categories could also be listed: historical, repentance, curse and creation.