Updated 2010-01-02. As I was browsing the Civil 3D Reminders blog searching for another solution I happened to glance at the Civil 3D 2010 Version post. After checkin my version after installing the Advantage Pack it seems this Version thing is still a moving target.

Roll back time a few months and in Civil 3D 2010 you could not go to the Help > About dialog to see what service pack version you have installed. Looks like there was a fix but now the Advantage Pack obscured that fix. So it is back to using the command line trick again. Below I show you how to get the build number which correlates to the service pack version.
Type AECVersion on the command line. You will get a long list of files and versions. Just focus on AeccBase DBX in the results. The third number is the build number.
1298 is the build number for the original shipping version with no service pack
This is a list of versions of Civil 3D 2010
No SP installed
CompanyName: Autodesk, Inc.
FileDescription: AeccBase DBX
FileVersion: 7,0,1298,0SP1 version
CompanyName: Autodesk, Inc.
FileDescription: AeccBase DBX
FileVersion: 7,0,1348,0SP2 version
CompanyName: Autodesk, Inc.
FileDescription: AeccBase DBX
FileVersion: 7,0,1387,0Subscription Advantage Pack installed version (requires SP2)
CompanyName: Autodesk, Inc.
FileDescription: AeccBase DBX
FileVersion: 7,0,2164,0
You can see we are up to Build 2164 after you install the Advantage Pack but the About dialog does not display the version you get Version: D.215.0.0, Subscription Advantage Pack. This makes version verification a less obvious process. I want to be able to browse the Autodesk web site to lookup info on a specific version based on what I find in the About dialog. For the moment we are stuck using the AECversion command to get a build number then refer to blog posts to get the version associated with that build number.
For your convenience I have posted links to service packs at http://www.advsurvey.com/Service_Packs.html
Small update:
SP3 version (on top of SAP)
CompanyName: Autodesk, Inc.
FileDescription: AecCBase DBX
FileVersion: 7,0,3025,0