Hands down, I would say Sitemasher.com is one of the most powerful web hosting and web-building platforms out there.  Built for collaborative work, SM charges big money for its services, but its reach is hard to match, delving into SEO, user role management, API connectivity, Flash, analytics, Photoshop imports, visual CSS customization, and more. 

Now featuring blogging, and encouraging the use of AdSense so you get paid for the work you do, SynthaSite has been expanding its tools and available templates.  In the upper middle ground of free web builders, SynthaSite lets you get beyond the godawful refrigerator art approach of basic website builders.  With a drag-and-drop interface, you can now give your blog an archive, "about me", category directory, blogroll, RSS and blog search widgets, and more.  The website side of SynthaSite lets people add photo galleries, video, widgets, forms, advertising, maps and an online store. 

Webon.com comes in a grudging third.  With a similar layout and drag-and-drop functions, it's the PC to SynthaSite's Mac.  It has Digg and Twitter widgets and a very small stable of user-submitted apps.  Hopefully this will change in the future but for now the number of user submissions can be counted on one hand with digits to spare.

At the bottom of the pile is Yahoo's Geocities.  Filled with Yahoo ads, the platform has improved somewhat since I wailed and gnashed my teeth trying to get a basic site together, but the whole setup whispers "try Yahoo web hosting instead, kid..."

And getting an honorable mention is this directory of building resources, http://toolkit.crispen.org/.  With links to Open Source Web Design's template archive, XHTML resources, clip art, stock photos, utilities and tricks, I'll be delving into the Toolkit a little more often.