Kudos to Martin Ferretti, a stockbroker by day and web junkie by night, has rolled out a nice starter guide to the major and some minor Linux distributions. That not to mention that his site also broadly serves as a resource to many other tools available to web professionals.
This is something I pine for often being a researcher myself, which is encouraging a broadening collection of data on open source for professionals to use in technology planning and spending. Ferretti has provided a good starter glossary of the various operating system flavors.
A logical next step would be a deeper look into the strength and weakness of each and which distros might target specific areas of technology use (web serving, desktop, file server and so on).
As an example, I initially used RedHat exclusively and really did not explore other flavors of Linux (1997-1999). However, having built various distros since I have found RedHat Enterprise ideal for file serving, mail serving and storage, Mandriva (Mandrake) as a good desktop model and Fedora and SUSE built as servers-only excellent for web serving with a simple and efficient patching models.
Not to ignore a loyalist favorite – I do like Debian and Slackware as it was how I was introduced to Linux in the first place. However, having worked with Linux in the enterprise pushes one toward RedHat and now Novell by default due to indemnification and support contracts.