For example, notice how the text isn't quite in the vertical center of the ComboBox.
Here's my XAML:
<Window x:Class="_24HoursBook.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="450" Width="350" MinHeight="450" MinWidth="350">
<Grid ShowGridLines="True">
<Grid.RowDefinitions>
<RowDefinition Height="0.15*" />
<RowDefinition />
</Grid.RowDefinitions>
<Image Grid.Row="0" Stretch="Fill" Source="Image/topBarBg.png" />
<StackPanel Orientation="Horizontal" Grid.Row="0">
<TextBlock Text="Platform"
Foreground="White"
FontFamily="Georgia"
FontSize="15"
Margin="10"
HorizontalAlignment="Center"
VerticalAlignment="Center"/>
<ComboBox x:Name="cmbPlatform"
Margin="10"
FontFamily="Georgia"
FontSize="15"
MinHeight="30"
MinWidth="140"
VerticalAlignment="Center">
<ComboBoxItem>All Platforms</ComboBoxItem>
<ComboBoxItem>Playstation 3</ComboBoxItem>
<ComboBoxItem>XBox 360</ComboBoxItem>
<ComboBoxItem>Wii</ComboBoxItem>
<ComboBoxItem>PSP</ComboBoxItem>
<ComboBoxItem>DS</ComboBoxItem>
</ComboBox>
</StackPanel>
<Image Grid.Row="0" Source="Image/about.png"
Height="16" HorizontalAlignment="Right"
VerticalAlignment="Center"
Margin="0 0 10 0" />
<ListView Grid.Row="1" Background="#343434">
</ListView>
</Grid>
</Window>
Add VerticalContentAlignment="Center"
to your combobox.