Is the Prayer of Manasseh among the Apocrypha? (Since my Norwegian Lutheran edition of the Apocrypha says so, and even notes that it is not in the RC Deuterocanon).
The prayer of Manasseh is part of the Vulgate canon, but is categorized (with Psalm 151, 1 Esdras, and 2 Esdras) as a non-canonical appendix to the deuterocanon; it also fully deuterocanonical in the Greek and Slavic Orthodox canons.
Actually, since the question has been raised, I'll just lay it out:
The following books are considered deuterocanonical in the Roman Catholic, Greek Orthodox, and Slavic Orthodox traditions, and apocryphal in the Anglican and high Protestant traditions:
Tobit, Judith, the Greek version of Esther, Wisdom of Solomon, Sirach (Ecclesiasticus), Baruch and the Letter of Jeremiah (the latter is sometimes Baruch ch. 6), the additions to Daniel (the Song of Azariah and the Prayer of the Three Jews, Susana, and Bel and the Dragon), 1 Maccabees, and 2 Maccabees.
The following are also fully deuterocanonical in the Greek and Slavic Orthodox traditions, and are Anglican apocrypha: 1 Esdras (a Greek version of 2 Chronicles 35-36, the whole of Ezra, and Nehemiah 8) and the Prayer of Manasseh. These two books are also in the Vulgate appendix.
Psalm 151 and 3 Maccabees are deuterocanonical among the Greek and Slavonic Orthodox.
2 Esdras is only deuterocanonical in the Slavic Orthodox canon, but is in the appendix of the Vulgate and is part of the Anglican apocrypha.
And last is 4 Maccabees, which is only part of (and is the only part of) the Greek appendix.
Note, also, that canonical Ezra is called 1 Esdras in the Vulgate, Nehemiah is called 2 Esdras in the Vulgate, Ezra and Nehemiah are together called Esdras β (beta) in the Greek canon, 1 Esdras is called 3 Esdras in the Vulgate and Esdras α (alpha) in the Greek canon, and 2 Esdras is called 4 Esdras in the Vulgate. And even more confusingly, 2 Esdras (Vulgate 4 Esdras) is actually a composite work made up of parts called 4, 5, and 6 Ezra, only the last of which is in the Slavonic (and known there as 3 Esdras). Have fun with that one. The best reference for this is the chart here:
Esdras - Wikipedia, the free encyclopedia
Also, for the deuterocanon as a whole, see pg. 1362 in the Oxford Annotated Study Bible NRSV 4th edition.