As of Version 6.0, LongestMatch has been superseded by the pattern object Longest.
Since Version 5.0 (released in 2003), LUBackSubstitution has been superseded by LinearSolveFunction.
As of Version 6.0, MeshRange has been superseded by DataRange.
As of Version 6.0, NotebookCreate has been superseded by CreateDocument, CreatePalette, and related functions.
As of Version 6.0, OpenTemporary has been superseded by functionality in OpenWrite.
Since Version 2.0 (released in 1991), Plot3Matrix has been superseded by ViewCenter and ViewVertical.
As of Version 6.0, PlotDivision has been superseded by MaxRecursion.
As of Version 6.0, PlotJoined has been superseded by Joined and ListLinePlot.
As of Version 6.0, PolygonIntersections has been superseded by various options for Export.
Random
(Obsolete Mathematica Symbol) As of Version 6.0, Random has been superseded by the functions RandomReal and RandomInteger.