It solely depends on what your requirement is.
If you are looking for evaluating SharePoint 2010 on a single system for checking foundation features you can install using Standalone mode with SQL Express with no additional overheads. In a 8 GB RAM system it should work just fine.
Power User and Enterprise Features
Incase there is a need to check enterprise capabilities like BI , Reporting Services , SharePoint Enterprise Search ,Excel Services, Visio Conversion - in that case you should preferrably go for a SQL Server 2008 R2 based farm. The sequence is mentioned below
Use a Windows Server 2008 Standard Edition and plan for service accounts
a. Install IIS 7.0 and .NET Framework
b. Install SQL Server 2008 R2 and leave Reporting Services to "Configure Later"
c. Install SharePoint on a single server farm mode with complete features.
d. Post installation of SharePoint configure reporting services in SharePoint Integrated Mode.
e. Plan for service applications and use only those that are needed as you will have limited system resources.
As time goes, SQL Server will take up around 2.5 to 3GB of RAM and workprocesses of SharePoint will consume around 1.5 GB including crawling and indexing.
You can install Visual Studio 2010 in the same system , however it will be a pain to debug by attaching your code to the worker proccess which will always render the system on a very low memory. It is advised for a RAM upgrade if possible incase you are planning to do development on this same system.
[All of the above constitutes the fact that Active Directory is residing outside this system. Incase you wish to create an Active Directory and Domain Controller role to this system , just ensure that you do all necessary clean up activities to efficiently manage memory like closing unnecessary plugins for browser , closing all open files in Text Editors and Office Applications if not in use, cleaning up pagefile etc.]