If you are the decision maker in your company and you are tasked with purchasing one or more servers to be used solely for SQL Server and solely as a data warehouse, be aware there are options outside of the usual ordering a server and internally installing the hardware, OS, and SQL Server.
Fast Track Data Warehouse is a reference configuration optimized for data warehousing. This saves an organization from having to commit resources to configure and build the server hardware. Fast Track Data Warehouse hardware is tested for data warehousing which eliminates guesswork and is designed to save you months of configuration, setup, testing and tuning. You just need to install the OS and SQL Server. There are currently ten vendors who offer servers based on the Fast Track Data Warehouse architecture, such as HP Fast Track Solutions for Microsoft SQL Server.
Taking it a step further, there are two appliances from HP that further customize the servers along with installing all the software: HP Business Decision Appliance (BDA) and Microsoft and HP Business Data Warehouse appliance (BDW). More info is at my blog Microsoft SQL Server Reference Architecture and Appliances.
If you are a larger company with a nice budget, and are looking at having a data warehouse in the hundreds of terabytes, then the Microsoft SQL Server Parallel Data Warehouse (PDW) might be an option. This is a massive parallel processing option where all the hardware and software is installed for you at your location. More info is at my blog Microsoft SQL Server Parallel Data Warehouse (PDW) Explained. Also check out HP-Microsoft SQL Server Appliance and Reference Architecture Solution Center.