=A1&char(10)&A2&char(10)&A3&char(10) ... etc.

Formula as RagDyer suggests or try a user defined function to get all in one
cell, space delimited.

Function ConCatRange(CellBlock As Range) As String
Dim Cell As Range
Dim sbuf As String
   For Each Cell In CellBlock
       If Len(Cell.text) > 0 Then sbuf = sbuf & Cell.text & " "
   Next
   ConCatRange = Left(sbuf, Len(sbuf) - 1)
End Function

Usage is:  =ConCatRange(a1:a20)

If you're not familiar with VBA and macros/functions, see David McRitchie's site
for more on "getting started".

http://www.mvps.org/dmcritchie/excel/getstarted.htm

or Ron de De Bruin's site on where to store macros.

http://www.rondebruin.nl/code.htm

In the meantime..........

First...create a backup copy of your original workbook.

To create a General Module, hit ALT + F11 to open the Visual Basic Editor.

Hit CRTL + r to open Project Explorer.

Find your workbook/project and select it.

Right-click and Insert>Module.  Paste the code in there.  Save the
workbook and hit ALT + Q to return to your workbook.

In a cell enter the formula as shown above in Usage is:

Gord Dibben  MS Excel MVP