This is the development stack I employ, and why I chosed it:
Being mostly a C# programmer (altough Ruby is growing on me) ASP.NET MVC is a pretty natural selection, being the most popular MVC framework for .NET. I don't think _not_ using a MVC framework for web development is very serious today. A MVC framework got so many benefits compared to for example WebForms I can't even begin, so i let Karl Seguin explain MVC vs. WebForms instead.
In a static language like C# you can't live without a dependency injection framework, i choose Autofac a long time ago and have stuck with it, i think most IoC frameworks are on par in the .NET world, but it seems to me that Autofac most often have the edge, coming up with new compelling features first.
Proven unit testing framework. Tried xUnit for a while but the poor tool support (in ReSharper and TeamCity) made me go back to nUnit, it just works.
There have been a lot of discussions on wether to use a mocking framework or not, but I like to write as lite code as possible when testing so a mocking is a perfect fit for me.
The Ruby community came up with Cucumber in which you write specifications in plain english (or swedish), and have become very successful. The idea has now been ported to .NET. Our customers love it!
For integration testing we use WatiN which automates Internet Explorer (and Firefox).
Mapping code is boring and error prone, automapper lets us do the entity->viewmodel mapping by ease.
Web error logging module, drop it in and all unhandled exceptions are mailed to us.
Proven logging framework for .NET, we use it in all apps for error and trace logging. Although, it's pretty ugly to configure through code.
PDF creator, a lot better API than iTextSharp, but don't got all the features of it.
Excel file creator, ported for java's POI, which the API suffers from, but got a lot of features (except rendering charts dynamically, which is a bummer.
Instead of referring to views and actions in code with "magic string" T4MVC creates strongly typed helpers for you.
A simple ORM which don't got the impressive feature set or the performance of nHibernate, but do got a supreme LINQ engine. Read my post on how to get the most out of Linq to SQL.
Don't do RMDBS with out a migration tool. It will ease a lot of the pain a static schema forces upon you. MigratorDotNet isn't maintained anymore but some alternatives are NMigrations and Fluent Migrator.
For all our javascript needs..
CSS framework, but will probably use 960 Grid System next time.
Continuous integration has always been a natural part of your workflow. TeamCity is very feature rich build management and CI server. It listens at our source code repository for changes, when some one commits anything it builds it, run all unit and integration tests and then deploys it to the staging/production servers, all with out us moving a finger.
Previously we used SVN with VisualSVN and hosted it ourself, but we've now employing Git, mostly because it's very good branch capabilities. Although a Git server is some what cumbersome to set up on a windows machine, so just signed up for GitHub, less hassel.
Unfortunately the Git support for windows is quite bad, so we use Cygwin (which "emulates" the linux api) to get the power of all those linux commands and applications, including Git right at our windows desktops.