The best affordable Adobe CS5 alternative is the academic version — e.g. CS5 Web Premium costs $1799 retail, $599 to upgrade from CS4 (more from earlier versions), and $549 brand new at Academic prices. Design Standard is $1499 vs $449. (There are even cheaper “Student & Teacher” options, but they can’t be upgraded and shouldn’t be used for commercial work.)
To understand how good a deal this is — Web Premium includes Dreamweaver, Fireworks, Photoshop Extended, Illustrator, and Flash. Coda, Photoline, and Intaglio would cost $280, and this doesn’t give you a Fireworks or Flash replacement. And to say that Photoline and Intaglio aren’t full replacements for Photoshop and Illustrator is a huge understatement.
If you aren’t eligible for an academic discoun, then things get more complicated.
The core components of Adobe CS5 are:
Photoshop: there’s no real alternative to Photoshop if you use Photoshop’s high-end capabilities. If you don’t use any of them then you can get away with a much cheaper program, such as Photoshop Elements, Photoline, Paintshop Pro, Acorn, Pixelmator, or even The GIMP. If you want natural media style painting abilities, Photoshop is actually not the best choice, and you should look at Painter or Art Rage (or Sketchbook Pro if you’re using a Tablet PC).
Illustrator: there’s a very good free alternative to Illustrator if you’re willing to live with an X-11 app, and that’s InkScape. Despite being X-11, it actually is very usable (more usable in some respects than Illustrator). Otherwise, there’s Intaglio, Lineform, Zeusdraw, VectorDesigner, and EasyDraw among others. (Sorry, but I’m not familiar with Windows alternatives, and Googling didn’t really help — ah Macs, so starved for software.)
Flash: while there are third-party Flash development tools (SWF is a pretty well-documented format), most are jokes or one-trick ponies. If you want to do serious work with SWF, you’ll need Flash, and you’ll probably need Photoshop and Illustrator since no other graphics tools are well-integrated with Flash.
After Effects: there are lots of alternatives to After Effects, but they’re all in the same price ballpark. If you’re a Final Cut Studio user, Final Cut Pro and Motion pretty much match After Effects’s feature set and are well-integrated. Similarly, if you’re an Autodesk/Avid user then why are you reading this paragraph?
Premiere: there are no good free video editing packages that I know of, although if you don’t need Premiere’s capabilities there’s iMovie and Final Cut Express (on the Mac).
Soundbooth: many, many alternatives, including the free and quite good Audacity.
On Location: there was a really awesome program called On Location, way back, that was essentially like Spotlight only over ten years earlier. This isn’t it. This is essentially a utility for capturing, adding metadata to, and otherwise managing digital footage when on a shoot, and I don’t know of any obvious alternatives (certainly no cheap ones).
Dreamweaver: if you’re not a hardcore Dreamweaver user (or, for example, a Cold Fusion developer), chances are you don’t need it at all. There are plenty of free and cheap web development tools out there. I’d recommend Coda for technically-savvy Dreamweaver users who are looking for an alternative and would like to give up their training wheels.
Contribute: I haven’t used Contribute, but from what I understand it’s a simplified web content editor aimed at people who essentially want to populate templates created by someone else. I don’t really like any of the desktop web development tools aimed at non-technical types, but if forced to pick one I’d probably pick Rapidweaver. Personally, I think this kind of thing is best handled using web-based content management tools such as WordPress.
Fireworks: Fireworks is a strange product. On the one hand most of its functionality is superfluous and it has a truly terrible user interface. On the other hand it has a number of — for UI designers — almost indispensable functions, notably pixel-centric vector drawing tools. If you need it, you need it.
InDesign: the only real alternative to InDesign is XPress (which, if anything, is more expensive and comes from a far more obnoxious vendor), unless you’re not using InDesign’s higher end capabilities, in which case your word processor (notably Pages) is a great alternative that you already know how to use.
Acrobat: again, if you need it you need it. Otherwise, not. Personally, I can’t stand Acrobat and don’t even want Acrobat Reader on my computers; for Mac users there’s Preview and the Print-to-PDF function both of which are far more pleasant to use than Acrobat (until you get technical). There are many better alternatives to Acrobat Reader, until you need to do something complicated, like fill in forms.