I'll quote my answer from a similar thread here
For database applications, starting
from DB up to Application level You
can have the DB of your choice, either
SQL Server, Oracle, Access, DB2,
Postgres ... etc Then the Data Access
Layer, is based on ADO.net that
basically can access your database
using any suitable driver/provider
like OLEDB, ODBC (is quite old),
Oracle Data Provider (ODP) ... which
gives native access to your database
specific functionality such as stored
procedures, which is not available if
you are communicating over ODBC. Then,
you can either use a code generator
like Linq to SQL (which comes for free
with VS 2008+) or other third party
code generators like LLBLGen Pro, and
others, or you can make O/R Mapping
using NHibernate or using more
sophisticated technology such as
Entity Framework which was just
release with .net 3.5 SP1 Then on top
of that you can develop your domain
objects using C# or the language you
like that consumes the infrastructure.
then on top of that, you can expose
your domain functionality using a UI
directly in this case ASP.net, or
expose them in the form of services
either SOAP or REST using WCF or
ADO.net Data Services (Which was also
released with .net 3.5 SP1, and were
built on top of WCF), then in case you
exposed the functionality in form of
services, you might need to
communicate with other services in a
workflow where you can use Windows
Workflow (WF), then you will need to
build a client that consume these
services, you can use develop as many
clients as your situation demands, for
example you can build AJAX client
using (MS AJAX framework + jQuery +
ASP.net) or you can build a RIA (Rich
Internet Application) using
SilverLight, or leverage the client
desktop capabilities and build a very
rich user interface using WPF/Windows
Forms client. So basically as you can
imagine from the long story above, how
.net can be the tool of choice to
build the end to end solutions from
the most bottom database level, up to
the server, down the wire to the
client browser and client machine.