First off, we're way beyond buying things now, unless you really want to spend the money. Adobe's Creative Cloud subscription service is well worth it, and you'll get more programs and services for the subscription fee per year than it would cost just to upgrade a suite version yearly, much less buy it outright.
Photoshop - Photoshop is the industry's leading graphics and image editing program. The Extended version will allow you to work on video and 3D files. You can do everything from photo retouching to original artwork.
Illustrator - Illustrator is more of an original artwork program; where Photoshop deals primarily with raster images, Illustrator is a vector artwork (i.e., you can resize any file without loss of quality). Examples of Illustrator use would be artwork done for magazines.
Fireworks - Originally a Macromedia creation, it was originally developed by them specifically for designing and deploying Web graphics in PNG format. There is no better program to do what it does, though since the Adobe-Macromedia merger in 2007, a lot of Fireworks' functionality has found its way into Photoshop and Illustrator.
Bridge - Bridge is essentially a file organizing program, and if you're a professional like me that has thousands of files (photos, videos, documents, images, etc.) it's indispensable. It's functionality is similar to Windows Explorer, except you can read Metadata of files, do batch processes (e.g., renames), and see/preview any type of file, even documents. Frankly, my life would suck without it.
Flash - Flash is another original Macromedia program, designed specifically to deliver web videos and animations with a lot of content and smaller file sizes. It is direct descendant of Macromedia's Director, which was (still is) a leading program for rendering DVD content.
Dreamweaver - a WYSIWYG & code editor, specifically designed to create websites. DW is one of the main programs that led Adobe to buy Macromedia; while Adobe at the time was the premier software company in the graphics creation/editing field, they knew that web design and animation were the future. The originally had their own web design program called GoLive, but to be blunt, it sucked big time. As they say, if you can't beat 'em, buy 'em - which is why Adobe bought Macromedia in 2007.
Since then, DW has become the standard for website creation, allowing for both front and back end coding. It's also meaning you can design visually or by hand coding. It has great tools for browser checking/code compatibility, and is great for overall site management. The latest version (CC) supports HTML5; CS6 does as well.
Acrobat - Acrobat Pro is Adobe's premier program for document packaging. Most people have used Acrobat Reader at some point; Acrobat Pro is the main program for file conversion to PDF, or creating original PDF's. You can also create original forms for online entry, as well as digital document review and signing.
InDesign - InDesign is Adobe's print/electronic media creation program. Everything from magazines, booklets, novels, newspapers etc., can be formatted for print publication using it.
Those are the main programs for most of the suites. Premiere and After Effects are for film and video production/special effects, and are industry standards in those fields. Adobe Audition is Adobe's program for audio mastering and DVD/CD/BD authoring.
Lightroom is Adobe's image editor / organizer for Photographers; it's essentially a digital darkroom, and was developed with that in mind. While it doesn't have the power of Photoshop, many of the filtering/enhancement features are the same. The organizing functions are similar to Bridge (it incorporates some of its elements) but has some features that go beyond it. It also has digital watermarking capability, with or without a plugin program (e.g. Digimarc).
For the other programs available with a Creative Cloud subscription, you're better off actually reading the various descriptions for them on the Adobe site:
http://www.adobe.com/
I can't overemphasize how much a CC subscription is worth it. I was a Master Collection user since CS3, and a full suite user since well before the merger. The money you save yearly even at the full cost of a yearly plan (about $50/mo) still winds up being less than it would cost you to buy a program or update it, and you get program updates free of charge when they release. You also get access to many more programs/features than you would if you bought a suite version. Web fonts are one of the more popular, as are Muse and Edge, which are new HTML5 based design and animation programs only available as standalone programs or with the CC.
You can view more here:
http://www.adobe.com/products/creativecloud.html?promoid=KAUBZ