Starcraft/Brood War [its expansion] = best strategy game available to date. Warcraft III is a newer and more user-friendly game (for instance, few more units can be selected at once [not really an issue, you'll tend to number your units in smaller groups than max for micro anyway], casting is more user-friendly in WCIII where telling a group to cast will have 1 unit cast, whereas in SC/BW you'll often have to quickly select individual casters to effectively use most spells), but SC/BW is still a better game than WCIII as far as strategy and balance. SC/BW has faster pace combat with a LOT of attention given to damage/armor types (gotta use the right units for the job, and there is pretty much ALWAYS a counter), whereas WCIII tends to be more "mass more stuff and throw it at them sooner than they can mass more stuff and throw it at you" oriented more toward whatever units are most imbalanced under the current patch. Heroes are huge in WCIII as well, which I've never met a SC/BW strategy game fan who was happy with. I'm not saying WCIII is awful but I know my opinion of this comparison of SC/BW and WCIII is shared by many, many who have played both games... Okay, to be honest, I never met anyone who disagreed.
Random sidenote: In addition to the regular games, WCIII has a newer and much more customizable map editor which makes for better custom maps. SC/BW's was powerful, but time offered a lot of advancements if you enjoy the custom maps. +what people said about customization: You can upgrade your weapons/armor for most everyone and research various other species/unit/building abilities, but nothing so unit-specific. The 3 races all have some different ways of doing things but the game is remarkably balanced with all of its counters.
I still remember working with StarDraft and a bunch of other mods for the SC/BW map editor to make it do all the things you could do to custom maps not available in the vanilla editor... You have no idea how long it took to randomize timers for wormspawns in a massive Dune map even with all my mods! [/rant]
I'm not sure how populated it still is online, but I have no doubt it's still easy to find a lot of games. SC2 is almost here so you might as well wait. Gameplay videos are available online.
lol @ shadowwolds and Blizzard never keeping to a release date. times ten.
[I wish I could obey forum rules]