AngleBracket[x, y, ...] displays as \[LeftAngleBracket]x, y, ...\[RightAngleBracket].
BracketingBar[x, y, ...] displays as |x, y, ...|.
Congruent[x, y, ...] displays as x \[Congruent] y \[Congruent] ....
Deletable is an option for Cell that specifies whether the cell can be deleted interactively using the front end.
DoubleBracketingBar[x, y, ...] displays as \[LeftDoubleBracketingBar]x, y, ...\[RightDoubleBracketingBar].
GridFrame is an option for grids that specifies whether a surrounding frame is drawn.
OverDot
(Built-in Mathematica Symbol) OverDot[expr] displays with a dot over expr.
OverHat
(Built-in Mathematica Symbol) OverHat[expr] displays with a hat over expr.
OverTilde[expr] displays with a tilde over expr.
PlusMinus[x] displays as \[PlusMinus]x.PlusMinus[x, y, ...] displays as x \[PlusMinus] y \[PlusMinus] ....