We mostly just do development and production.

I don't really understand the question.

development and production is an absolute minimum for a professional web site - how else do you build something new without breaking the live site.
Staging is only really needed when there is a team who will individually be working on different bits so you need a live testing environment to ensure that conflicts in development won't break the live site.
If you are a one-man op then dev and prod are sufficient, unless you are really anal ;)

Exactly. I work with one company that has a 3 person tech team, and they go directly from a testing environement to live. I work with another that has a 60 person team, and they go development > staging > production

tedster - Without giving too much info can you give a high level view of what happens on each stage? I understand development and production, but what happens on stagging. When do you have QA and client/customer (internal) review?

Staging is the step where internal QA happens. A new version of the site is pushed to staging about once a week during any redesign or development process. Then a week before launch, certain preferred customers are also given incentive to kick the tires. That can be a very hectic week, by the way!

I almost never review anything until it hits the staging server. Rarely someone will ask for input from something on the development server -- I can think of twice in the past year.

I currently have a local development environment plus live.

Despite not being a team I will be moving to having a test environment inbetween. I am moving to automate various tasks (uploading common code to multiple websites, database schema changes etc) and I want to be able to run that against a test environment before I run it against live.

The test environment will probably be virtual though.

We have the following (for one site application):

Sandpit
Development
System test
Staging
Pre-Production
Production

Sandpit
A play pen where we can try out crazy ideas.

Development
For current business-as-usual or project developments

System test
System testers do thier testing here

Staging
Used for content publishing practice (by the client) - it can then be deployed to PP and Prod from here.

Pre-Production
Mirror of prod (in hardware terms too), used for testing architectural issues and also acts as a backup should a part of Prod fail.

Production
Obviously our production site for the public

In addition to these it is a little more complicated since sometimes we might introduce more machines in say Development if we have more than 1 stream of work on at once. Also, sandpit and dev share the same CMS database. Likewise with databases, some environments may have dedicated database servers or some might share one. the other variant is we have 1 physical server with many instances of a database on it.