The SQL Server Analysis Services Team recently announced the release of their DAX Editor for SQL Server as a Visual Studio 2010 extension. Until this point, there hasn't been an editor for DAX queries that supports syntax highlighting, IntelliSense, and other basic Visual Studio Features.
Data Analysis Expressions, known as DAX, is a language used to construct formulas in PowerPivot tables and Excel PivotTables. DAX syntax is similar to that of Excel formulas, and it can be used to create calculated columns and measures in PowerPivot. The PowerPivot Window (like Excel) uses a formula bar for manual entry of DAX formulas.
The DAX Editor for SQL Server adds familiar Visual Studio editing features, such as auto-formatting, IntelliSense, syntax highlighting, autocomplete, error highlighting, F1 help, and brace matching. According to the Analysis Services Team, "The DAX Editor can be used to write standalone DAX queries or you can use the DAX Editor to extract measures from a BIM file, edit measures, and then save measures back to a BIM file."
The DAX Editor is available as an officially-unsupported sample, and the Analysis Services Team is requesting feedback on the new project. More information and a download can be found at CodePlex.