Since Version 3.0 (released in 1996), ReplaceHeldPart has been superseded by ReplacePart.
Since Version 2.0 (released in 1991), ResetMedium has been superseded by SetOptions.
SequenceForm has been superseded by Row and Text.
Shading
(Obsolete Mathematica Symbol) As of Version 6.0, Shading has been superseded by ColorFunction.
As of Version 6.0, ShortestMatch has been superseded by the pattern object Shortest.
Since Version 5.0 (released in 2003), SingularValues has been superseded by SingularValueList and SingularValueDecomposition.
Since Version 2.0 (released in 1991), StartProcess has been superseded by Install and MathLink.
As of Version 6.0, StyleForm has been superseded by Style.
As of Version 6.0, StylePrint has been superseded by Print[Style[expr, " style"]].
Since Version 3.0 (released in 1996), Subscripted has been superseded by RowBox, SubscriptBox, etc.