Q:

Excel automation from database, what's the Best Technology to do that? 

I want to have Excel reports generated from the database. 
What do you think is the best Technology to use for Excel automation ? 

Consider :
> Full Excel API Support is a must. 
> Cross Platform solution preferable. 
> Programmer's efficiency is high priority. 
> Mono development is welcome, if that provides an edge. 
> Open Source solutions are welcomed. 
> VB.Net, C#.Net or something else ? 
> What build environment to use, MSBuild or NAnt or something else ? 

Please throw your experiences and advises for my project !! 
Its going to be massive reporting project, with a lots of Excel API's to be exploited. 

A:

Your question has lots of technical requirements but not any business requirements, If the users want some reports from a DB that they can view / manipulate in excel then there are probably better ways to do it than using the excel API. 
If you want to generate reports I'd suggest using something built for the job rather than implementing your own solution.  If your SQL environment is MS SQL Server then SSRS would do the job, in fact you can use SSRS with other Databases if you want including mySQL and Oracle.  If not then this answer has some open source solutions. 