What are good sources (information and/or available tools)I can use to
effectively draw vistors to my website?

What kind of a site is it?  There are different marketing strategies
for different types of sites...

I currently have 2 sites, one where people can order product, and the
other that describes the opportunity. However, to access them, you
must know their web addresses beforehand. I was thinking about the
possibility of creating another site(s) that people would be led to as
the result of searches (i.e., ?diabetes?) that would then link to the
2 original sites.

the best way to draw users to your website/websites is first making
them known to the people-that is making them popular.for this you need
to post the address of your website in different forums which are
there on the web,when you post the address of your websites also give
a short introduction about them like what are they about and how can
benefit by visiting them
another way is to make pamplets about your website and distribute them
among the peole,another way is to make stickers with the name of your
site and paste then near places where a lot of people visit-it will
defenately arouse their curosity
and they will log to see what is it about
another cheap way is to go to chat rooms of yahoo,msn,icq and other
public chat rooms and type the address of your site-this will surely
draw a lot of visitors to your websites