Welcome to the forum.
As you have Dreamweaver (and Flash?), and are doing Web work, you can probably get by with Photoshop Elements. It is much less expensive, and other than commercial printing, CMYK support, and the abiltiy to create Layer Sets, such as used in Adobe Encore DVD/BD Menus, has most of the features of PS.
If, in your Web page design, you are also interested in streaming Video, you might wish to consider the PSElements & Premiere Elements bundle. PrE is sort of the "little cousin" to Premiere Pro, but is a very powerful program.
Thank you Bill
It was a daunting question as simple as it may seem. Thanks mate
Yes. It would seem that with only three "flavors" of Photoshop, one could determine immediately which version would suit their needs. However, it can be tough to decide. To me, Photoshop Elements is the best "deal," as it has much of the power of Photoshop, but at a greatly reduced price. To me, the downside is that it is designed as a bit more of a Big Button program, with much automation, or semi-automation, with less direct user control. For its target audience, that is probably a great thing, but I really like my control. Still, it will do much of what its big-brother can do, and at a steal of a price. For me, the lack (unless it has been added in PSE 10) of the ability to create Layer Sets is a non-starter, since I do a lot of DVD/BD Menu creation. PSE can edit Layer Sets, but not create them. Were one to need that function, and buy PSE, they would be greatly disappointed.
The biggest difference between Photoshop & Photoshop - Extended, is some 3D and Video handling. If one needs those functions, then Extended is a must have. If they do not, then Photoshop will do the trick (or perhaps Elements). Now, if one has Photoshop - Extended, and does a lot of Video and animations, then they should probably also consider Premiere Pro, and maybe even AfterEffects for heavy animation compositing.
If they do not need ALL of that power (comes with a fairly hefty price tag), then there is the PSElements & Premiere Elements bundle.
If one does need the power, Adobe bundles the "big-boys" into the Production Premium (note: that name changes a bit, from time to time, but it is the bundle below the Master Collection, which has Web development software too). One gets almost anything that they would need, and it has been typified as buy one, and get ten free. While that is a bit of an exaggeration, it is a real "deal" in my book, as it has PS - Extended, PrPro, AE, Encore, OnLocation, Illustrator, and a few more. Still, that PSElements & PrElements bundle can do an awful lot.
I have never seen a chart with ALL of the differences between the various Adobe programs (just a few general ones), so doing, as you are, and asking, is probably the best course of action. It's just that a definitive answer is a bit hard to come by.