From our comments here is something you can use:
Sub random()
Dim used_rows As Integer
Dim random As Integer
Dim cell_array() As Integer
used_rows = Sheet1.UsedRange.Rows.Count
ReDim cell_array(used_rows)
For i = 1 To used_rows
cell_array(i - 1) = Cells(i, 1)
Next
random = Int(Rnd * (used_rows))
MsgBox cell_array(random)
End Sub
You can go ahead and change MsgBox to whatever you like, or set like Cell(1,4).Value = cell_array(random), or however you'd like to proceed. It will be based off the number of rows used. Though depending on how you implement your spreadsheet the code might have to be changed a bit.
Here's the update code from the suggestions from the comments. Also remember to use Randomize() in your form initialization or WorkBook Open functions.
Sub random()
Dim used_rows As Integer
Dim random As Integer
'Multiple ways to get the row count, this is just a simple one which will work for most implementations
used_rows = Sheet1.UsedRange.Rows.Count
random = Int(Rnd * (used_rows))
'I use the variable only for the reason that you might want to reference it later
MsgBox Cells(random, 1)
End Sub