Automake supports Vala since 1.11
Autovala, a program that automates the creation of CMake files for Vala projects.
BuilDj Software Project Description Format
Waf based template project
Emacs mode available.
highlight.js - Client side syntax highlighter (JS+HTML)
medit is a light-weight programming and around-programming text editor with vala syntax highlighting.
MoinMoin Wiki parser.
Pygments has a lexer since version 1.1.
Sublime Text 2 bundle to add Vala support.
There are various projects in various states of stability in order to provide IDE support for Vala:
Atom - Vala package for Atom editor
GNOME Builder - Builder has extended support for Vala in what will become 3.18.1. This includes a symbol tree, as you type error highlighting, auto completion, auto indentation, and "Goto Definition".
Geany is an integrated development environment with support for vala syntax and code completion.
Netbeans - Plugin for the Netbeans IDE for Vala
Valama - An IDE with glade editor & symbols navigator
Vala Toys for gedit - Vala plugin for gedit
Valencia - Vala plugin for gedit
Val(a)IDE is an integrated development environment for Vala, developed with Vala. (valide is no longer supported)
Valadoc - generate documentation from VAPIs, GIRs and other files
Gcovr - code coverage reports, use the --debug switch with valac to include source file line numbers