SharePoint:Content By Query Webpart QueryOverride Filter data based on multiple content types

Content Query webpart series:
Part 1: Configuring SharePoint 2010 CQWP

Part 2: CQWP PageQueryString and PageFieldValue
Part 3: CQWP XSL customizations
Part 4 : CQWP QueryOverride

Complex queries can be created using CAML Query builder and used in CQWP using QueryOverride property.
Following query will filter data of content type "Announcement" and "Company Announcements".
<property name="QueryOverride" type="string"><![CDATA[<Where><Or><Eq><FieldRef Name="ContentType"/><Value Type="Computed">Company Announcements</Value></Eq><Eq><FieldRef Name="ContentType"/><Value Type="Computed">Announcement</Value></Eq></Or></Where>]]></property>