Well, as far as plain HTML goes, there really isn't anything that's all that cool about it. All you can really do is organize stuff, put images and
text, and occaisionally change colors of parts of the page.
Most likely the stuff you're seeing on the web that's catching your eye is either Flash or Javascript. Maybe an occaisional Java applet or
something, but those are getting fewer and further between. Also, you can get some really killer stuff going on with Cascading Style Sheets--CSS--if
you know what you're doing.
A decent site to check out for Javascript, CSS, and basic HTML is
www.webmonkey.com. They have a decent code library; go to the authoring
section on their site.
www.w3schools.com is a decent all-around reference, and if you're wanting a more technical approach, there's
www.w3.org, the guys who keep track of all the different standards. There's also
_javascript.com and
_javascripts.com (note the plural in the second one.)
dynamicdrive.com is another decent one.
If you're wanting to do Flash stuff for your sites, you'll need to buy the Flash program by
Macromedia. I
think there's a couple of small, freeware programs here and there that'll let you do small things, like buttons and menus, but if you're wanting
anything that's really neat, you need to get the latest version from Macromedia.
flash-kit.com would be a good place to check out some
examples of what you can do with Flash.
Of course, you can still do a really attractive, catchy site with plain ol' HTML; it's just a matter of knowing what you want and knowing how to do
it. The webmonkey link above is a really good site to start with for a reference. Another invaluable method of learning is finding a site that has
something you like, then click on the View menu button, then click on Source. The vast majority of the time it'll show you all the HTML and stuff
for the page. A few people have figured out ways around this, but that's by no means common.
Good luck
Hope I helped some.