Visual Studio 2005 has a number of new improvements over VS.NET 2003. One of the big ones is that FrontPage Server Extensions are no longer required. In fact, Microsoft has embraced a new Internet standard -- they're really leading the pack on this one -- called File Transfer Protocol, or FTP. Ok, so maybe it's not that new, but it is supported (finally) by VS2005, along with a number of other methods for connecting to webs.
No more project files (for websites)
VS2K5 uses a directory-based model that no longer requires project files. You can edit any web anywhere. The performance impact of this change is pretty dramatic for big sites.
No More Single DLL Per Website
It's no longer necessary to build the entire web application into a single DLL, which made team-development of a single web app a nightmare. In fact, by default you're never building web pages at all anymore. It's very much just like it was back in the 'good old' ASP 3.0 days where to build a web form you just saved the file, uploaded it, and to test you viewed it in your browser. Everything is compiled server-side. Now you can modify a single page in the application and not worry that you'll have to rebuild the whole thing (and restart the whole app due to changes in the bin folder) just to touch one page.
HTML Source Preservation
In theory, and so far the theory is proving to be true from my experience, the tool will never, ever, ever reformat or mangle your HTML code. It does support some reformatting features, but you specify when and if you use these. There is also going to be built-in support for a variety of schemas against which the HTML can be validated, including XHTML.
No longer limited to codebehind files, you'll now see intellisense in HTML view, including for HTML elements. In page directives. In <script runat="server"> blocks within HTML, etc. All of these work in the March04 preview build. A big one that's not there yet but should be before release is web.config intellisense (but there should also be a web.config GUI editor, too, by then).
HTML Tag Navigator
Displays nesting depth at the bottom of the editor (e.g. <html><body><form><table> to show that you're inside a <table> tag). Will also support collapsing/expanding of HTML elements, similar to #regions in code.
Built-In Test Web Server
No longer requires IIS, so XP Home users can develop ASP.NET pages. The test web server is built on Cassini, which ships with the free Web Matrix tool (and for that matter, a lot of the ideas that went into VS2K5 came from Web Matrix). Only responds to requests from localhost, and not optimized at all for any significant traffic, this is purely a test web server.