How can I find last row that contains data in a specific column?

How about:

Function GetLastRow(strSheet, strColumn) As Long
    Dim MyRange As Range

    Set MyRange = Worksheets(strSheet).Range(strColumn & "1")
    GetLastRow = Cells(Rows.Count, MyRange.Column).End(xlUp).Row
End Function

Regarding a comment, this will return the row number of the last cell even when only a single cell in the last row has data:

Cells.Find("*", SearchOrder:=xlByRows, SearchDirection:=xlPrevious).Row

You should use the .End(xlup) but instead of using 65536 you might want to use:

sheetvar.Rows.Count

That way it works for Excel 2007 which I believe has more than 65536 rows