To bind to the current DataContext in XAML you can use:
How do you do this using a converter in the mix?
Dot sign also provide DataContext Binding for SL developers
<TextBlock Text="{Binding Path=.,Converter={StaticResource converter}}" />
Simply omit the path:
<TextBlock Text="{Binding Converter={StaticResource converter}}" />
Ah wait - I notice your question is tagged with Silverlight. Does this not work in Silverlight? If not, you may need to use the expanded syntax:
<TextBlock>
<TextBlock.Text>
<Binding Converter="{StaticResource converter}" />
</TextBlock.Text>
</TextBlock>