I think photoflex offers very good value for the price. http://www.photoflex.com/
If you sign up for their newsletter they e-mail lighting lessons that are very good (of course, it is always promoting their equipment).
I've also found that eBay can be a very good source for used softboxes etc. It seems like a lot of people buy these, don't use them much and then sell them. Just compare the prices to new to make sure you are getting a good deal.
One thing you can learn from my mistakes – buy the Manfrotto umbrella brackets http://www.adorama.com/BG2905.html
. They are slightly more expensive than other brands, but very well made and there are few things more embarrassing and distracting than having a soft box or umbrella keep shifting while you are trying to shoot. Some of the cheaper brands and designs just don't hold up.
You mention sync cables. I know that professionals prefer radio triggers and if you can afford them they are great. But honestly, I've had very good luck with infrared triggers, even in bright sunlight. Yongnuo makes a knock-off of the Canon infrared trigger that is cheap and I've found very effective. If I were doing this for money, I'd invest in radio triggers. But I'm not.
If you want some fun things to play with, the Interfit Strobies Kit http://www.adorama.com/PASTR100.html
gets you a lot of toys for not a lot of money. I wouldn't buy them until you got a couple of umbrellas and a softbox, but if you want to experiment, they are an affordable way to do that. Just be sure to order the correct adapters for your speedlite.
Finally, let me just say this: you can do a lot worse than a single umbrella. Really, you can make beautiful flattering portraits with just one umbrella, adding other tools as you learn. A decent umbrella, a Manfrotto bracket and a solid lightstand will go a long way.