TFCD

I'm not new to photography, but I am expanding. I've never used external lighting before, but I am looking at investing.

What would you suggest as an entry level step up?

I want to use something in addition to my 420EX.

I do a lot of "street shoots" and sometimes there is nothing to bounce the light off and a "flash in the face" is to much.

Sorry if this sounds like a newb question.

What is the difference between strobes and umbrella lighting? Which would suit my needs, as I've described, better?

There is not difference between strobe and umbrella. The umbrella is simple a modifier between your strobe and the subject. Some of the best online examples I've seen of shoots like you're doing are on Youtube. Do a search there for "Bert Stefani" and his "confessions of a photographer" series.

For start up lights, you may want to look at Alien Bees. While I have never used them, I do know ppl who have, and they've been very happy with them. Personally, for myself, I have made a heavy investment in Elinchrom lighting (just got their 400ws Quadra portable battery powered system...very nice, but very expensive). If you plan on sticking with studio type strobes, I think it is well worth the extra money to go into high quality systems. They will last, and if you change your mind and it is not for you, then you may have better reselling value in them.