I agree that the Behringer is a great option. Don't be discouraged by the inexpensive price. It is a quality product, well researched by the members here.
B&H is a good source with a good reputation though you may find it for not too much more at your local pro audio store (Guitar amps, etc. - These speakers are designed as recording studio monitors)
http://www.bhphotovideo.com/c/product/321847-REG/Behringer_B2030P_B2030P_2_Way_Passive.html
However, I would recommend a better sub than the Dayton. With your budget of $550 for speakers and sub, the speakers will cost about $130. I would apply the remaining ~400 to the sub.
Dr. Hsu makes what are probably the most musical subs available in this price range.
I'm assuming your interest is primarily music (as opposed to gaming or Home Theater) and your room is not too large (not over 3000 cu. ft.). For gaming or HT, subs are expected to rumble your guts on explosions.
http://www.hsuresearch.com/products/stf-2.html
Make sure you check the dimensions of the sub and envision it on your room.
The STF-1 is a bit less expensive, but for only $50 difference, I would stick with the STF-2. For music, this will hold you for a good while.
Edit: If you have any questions about the subwoofer, don't hesitate to contact HSU via email. Their communication is outstanding and they are the rare company that is more interested in helping you realize your objective rather than maximizing their profit off of you!