A little birdie whispered in my ear about a nice roundup of the sundry ways to watch soccer online over at SoccerLens, including both pay and free options. I'd also lob in the domestic footie grenade that is MLSLive.tv--an excellent value at $20 for pretty much everything that's not on ABC, ESPN, HDNet, or FSC.
Those of you with a Jesse James complex or a tight budget might benefit from a visit to MaxXed Football Forums or HPI's torrent tracker (dubious legality, so no direct links, but Google is an able partner in "crime"--or so I've heard). If all else fails, haunting the BigSoccer forum for a team or nation about to kick off a game will often provide the streaming goods.
I've got some other options in my kitbag, but let's just close with a shoutout to actually attending soccer matches, whether they involve internationals, MLS, trips abroad, or your kid's youth side. Tiny windows on stuttering bits and bytes are those hard-to-reach veins that junkies just have to tap. But nothing is better than mainlining the live experience.
Still, if you've got that itch . . .