Have the ability to execute builds and supply dynamic properties through the Command Palette.

For build systems like Ant, Maven, and Gradle it is very common to supply various targets or tasks to the build system depending on your workflow, not to mention switches to change default behavior.  This is something that is not well support by having the build-system configuration file be the only source for defining build tasks.  I think having a Command Palette build command is a very useful built-in feature at a basic level and then have it support dynamic arguments would be really useful.