I agree with Wendy's suggestion to rent for a while and develop a feel for what you like. I also am a big fan of college dive clubs as it is a great way for people to get started and have access to inexpensive gear rentals.
With regulators and BC's in particular, personal preference counts for a lot. What makes a regulator or BC ideal for a particular diver has at least as much to do with "feel" as with quality or performance numbers and the only way to experience this is to actually use the reg or BC in the water by either renting or by demoing the equipment in a pool.
If you are in a "have to buy it right now" situation, many local dive shops offer package deals that can be very competitive with on-line retailers with the added benefits of better warranties and service. Package deals often allow local dive shops to effetively discount expensive items like regulators and BC's that they may otherwise be restricted from discounting due to dealer agreements. Most should also be willing to make substitutions in the package to allow a little more choice of what you want. If not, find another shop.
Local dive shops often frequently sell their rental gear every one to two years, so if you rent it and like it, odds are you may be able to buy it at a very good price.
I am not a fan of on-line stores, particularly for new divers. It's hard to tell what you are getting on-line and even harder to tell if it will fit and/or be appropriate for what you plan to do.
Where ever you shop, I would suggest buying gear from established manufacturers with a large dealer network to ensure that you will be able to find support and service for what you buy where ever you end up going. I like Scubapro and Aqualung in this regard but I am also a bit biased and there are probably other companies that may offer equal levels of service.