Extracy unique item and them use COUNTIF:
Excel 2010<table rules="all" style=";background-color: #FFFFFF;border: 1px solid;border-collapse: collapse; border-color: #BBB" cellpadding="2.5px"><colgroup><col style="background-color: #DAE7F5" width="25px"><col><col><col></colgroup><thead><tr style=" background-color: #DAE7F5;text-align: center;color: #161120"><th></th><th>A</th><th>B</th><th>C</th></tr></thead><tbody><tr><td style="color: #161120;text-align: center;">1</td><td style=";">List</td><td style=";">Unique</td><td style=";">Count</td></tr><tr><td style="color: #161120;text-align: center;">2</td><td style="text-align: right;;">12/3/2011</td><td style="text-align: right;;">12/3/2011</td><td style="text-align: right;;">1</td></tr><tr><td style="color: #161120;text-align: center;">3</td><td style="text-align: right;;">1/4/2012</td><td style="text-align: right;;">1/4/2012</td><td style="text-align: right;;">2</td></tr><tr><td style="color: #161120;text-align: center;">4</td><td style="text-align: right;;">1/4/2012</td><td style="text-align: right;;">3/8/2012</td><td style="text-align: right;;">1</td></tr><tr><td style="color: #161120;text-align: center;">5</td><td style="text-align: right;;">3/8/2012</td><td style="text-align: right;;"></td><td style=";"></td></tr><tr><td style="color: #161120;text-align: center;">6</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style=";"></td></tr><tr><td style="color: #161120;text-align: center;">7</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style=";"></td></tr><tr><td style="color: #161120;text-align: center;">8</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style=";"></td></tr><tr><td style="color: #161120;text-align: center;">9</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style=";"></td></tr><tr><td style="color: #161120;text-align: center;">10</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style=";"></td></tr></tbody></table>
Sheet1
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Worksheet Formulas<table rules="all" style="border: 1px solid;text-align:center;background-color: #FFFFFF;border-collapse: collapse; border-color: #BBB" cellpadding="2.5px" width="100%"><thead><tr style=" background-color: #DAE7F5;color: #161120"><th width="10px">Cell</th><th style="text-align:left;padding-left:5px;">Formula</th></tr></thead><tbody><tr><th style=" background-color: #DAE7F5;color: #161120" width="10px">C2</th><td style="text-align:left">=COUNTIF(
$A$2:$A$17,B2)</td></tr></tbody></table></td></tr></tbody></table>
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Array Formulas<table rules="all" style="border: 1px solid;text-align:center;background-color: #FFFFFF;border-collapse: collapse; border-color: #BBB" cellpadding="2.5px" width="100%"><thead><tr style=" background-color: #DAE7F5;color: #161120"><th width="10px">Cell</th><th style="text-align:left;padding-left:5px;">Formula</th></tr></thead><tbody><tr><th style=" background-color: #DAE7F5;color: #161120" width="10px">B2</th><td style="text-align:left">{=INDEX(
list,MATCH(0,COUNTIF($B$1:B1,list),0))}</td></tr></tbody></table>
Entered with Ctrl+Shift+Enter. If entered correctly, Excel will surround with curly braces {}.
Note: Do not try and enter the {} manually yourself</td></tr></tbody></table>
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Workbook Defined Names<table rules="all" style="border: 1px solid;text-align:center;background-color: #FFFFFF;border-collapse: collapse; border-color: #BBB" cellpadding="2.5px" width="100%"><thead><tr style=" background-color: #DAE7F5;color: #161120"><th width="10px">Name</th><th style="text-align:left">Refers To</th></tr></thead><tbody><tr><th style=" background-color: #DAE7F5;color: #161120" width="10px">list</th><td style="text-align:left">=Sheet1!$A$2:$A$200</td></tr></tbody></table></td></tr></tbody></table>