I've been helping people with SQL Server for quite a while now, and I continually hunt for information regarding what features are available in which edition of SQL Server.  Well, SQL Server 2008 has improved in many ways, including new edition packages that will allow you to choose a solution that is going to meet your needs and stay within your budget.  To me, the even better part about SQL Server is how easy it is to move between editions.  For example, if I create a database for a customer on my Vista machine running SQL Server 2008 workgroup edition, I can easily detach the database, burn it to a CD and move it to a customers Enterprise edition without any headaches.

To keep everyone from searching I've included the link to find it online:  http://msdn.microsoft.com/en-us/library/cc645993.aspx.  Personally, this is much easier to navigate and find what you need / get in each edition as compared to the listing created for SQL Server 2005 (http://msdn.microsoft.com/en-us/library/ms144275(SQL.90).aspx) .  As before, you have a great selection of 32 or 64 bit installs, but remember, if at all possible, in your production environment, go 64 bit if possible.