ISBLANK

A value of any type                

=ISBLANK(A1)        

Returns TRUE if cell is empty

ISERR

A value of any type                

=ISERR(H1)

Returns TRUE if the cell contains any error value except #N/A

ISERROR

A value of any type                

=ISERROR(A7)

Returns TRUE if the cell contains any error value (#N/A, #VALUE!, #REF!, #DIV/0!, #NUM!, #NAME?, or #NULL!).

ISLOGICAL        

A value of any type

=ISLOGICAL(C3)

Returns TRUE if the specified value refers to a logical value

ISNA

A value of any type

=ISNA(E5)

Returns TRUE if the cell contains #N/A (value not available) error value

ISNONTEXT

A value of any type

=ISNONTEXT(D4)

Returns TRUE if the cell does not contain text.  Returns TRUE for blank cells

ISNUMBER        

A value of any type

=ISNUMBER(A2)

Returns TRUE if the cell contains a number

ISTEXT

A value of any type

=ISTEXT(D1)

Returns TRUE if the specified cell contains text