One of thing that you want to do with a release build is automatically increment your version numbers.  Most approaches to this problem recommend using MSBuild to autogenerate the AssemblyInfo.cs file.  Although that certainly works, I prefer not to have to do that for every project.  Instead, each of our projects references a single CommonAssemblyInfo.cs file.

When TeamCity builds a release build, it is configured to the IncrementVersion task:

   1: <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">

   2:     ...

   3:     <Target Name="UnrestrictedExecutionPolicy">

   4:         <Exec Command="powershell set-executionPolicy unrestricted&quot;" />

   5:     </Target>

   6:     <Target Name="IncrementVersion" DependsOnTargets="UnrestrictedExecutionPolicy">

   7:         <Exec Command="PowerShell .\incrementVersion.ps1 $(build_vcs_number_1)" />

   8:     </Target>

   9:     ...

  10: </Project>

The $(build_vcs_number_1) property tells TeamCity to the current revision number from the first source repository attached – in my case SVN — to the project (most projects will only have one repository attached).  Then, we execute a simple Powershell script to replace the file version number:

   1: $buildNumber = $args[0]

   2: (Get-Content ..\src\CommonAssemblyInfo.cs) | Foreach-Object {$_ -replace "(\d\.\d\.\d)\.\d*", "`$1.$buildNumber"} | Set-Content ..\src\CommonAssemblyInfo.cs

If you are more comfortable using a MSBuild task for regex replacement, there is a RegexReplace task that is part of the MSBuild Community Tasks.  For my build, we do not need any other custom tasks, so it was preferable to just use a simple PS script.