SortedList values = umbraco.cms.businesslogic.datatype.PreValues.GetPreValues(umbraco.cms.businesslogic.datatype.DataTypeDefinition.GetAll().First(dtDef => dtDef.DataType.DataTypeName.ToString() == "productCategories").DataType.DataTypeDefinitionId);

You might want to watch for front end use though.. as I think this will always hit the database....

Thanks for that Mike, I am new to both Umbraco and .Net but after I posted I further researched and found that the PreValues.GetPreValues was the route to go. However when I used your code the following error appeared:

System.InvalidOperationException: Sequence contains no matching element

When I use the following code (taking out the reference to the name of the Data Type) where 1964 is the nodeID of my Data type I do not get an error:

var prevalues = umbraco.cms.businesslogic.datatype.PreValues.GetPreValues(1964);
foreach (var item in prevalues){
    <p>@prevalues</p>
}

The output is the correct number of paragraph tags as are prevalues in my data type but they all just say:

System.Collections.SortedList

Do you know the way of calling the prevalues into the paragraph tags?

Enumerating a SortedList is not very intuitive - but you can do it like this:

var prevalues = umbraco.cms.businesslogic.datatype.PreValues.GetPreValues(1964).Values;
var enumerator = prevalues.GetEnumerator();
while (enumerator.MoveNext()) 
{
  <p>@((PreValue)enumerator.Current).Value</p>
}

I tried your code Andy but for some reason no paragraph tags were being rendered onto the page (inside the while loop). However I seem to have got what I wanted with this piece of code, not sure if it is correct but helped me and may help others

@using System.Xml.XPath
@using umbraco.MacroEngines
@inherits DynamicNodeContext

@{
    XPathNodeIterator iterator = umbraco.library.GetPreValues(1964);
    iterator.MoveNext();
    XPathNodeIterator preValues = iterator.Current.SelectChildren("preValue", "");

    <ul>
    @while (preValues.MoveNext())
    {
        string preValue = preValues.Current.Value;

        <li>@preValue</li>                      
    }
    </ul>
}

Basically this example on the Umbraco website: http://our.umbraco.org/wiki/reference/umbracolibrary/getprevalues

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