-DO NOT BUY BOSE. You can do much better for the same or just about as much as Bose costs. Also, there are rumors that Beats by Dr. Dre is going to get into the speaker game. If so, DO NOT BUY BEATS SPEAKERS.
-Listen to speakers in person. Be sure to audition speakers without a subwoofer activated or connected (to see if they can produce adequate bass by themselves). Turn the speakers up very loud to see if it can handle high volume without distortion and turn it down very low to see if it can produce subtle and more accurate sound.
-Bring along your own music is listen to a range of pieces from heavy bass like trance and house, vocal pieces with female voices (female vocals are probably the most difficult sounds to reproduce accurately), softer and more subtle pieces that emphasize mids and highs such as orchestral, and heavy rock and guitar pieces.
-Stick to well known brands such as B&W, Klipsch, Boston, Definitive Technology, Mirage, Energy, etc., Of course, you can spend more on elite brands such as Vienna Acoustics, Paradigm, Martin Logan, etc., but the previous brands can be just as good. If you can't spend that much, stick to less expensive yet very good brands such as Polk Audio, Wharfedale, etc. Also, generally, the brands that make decent electronics (Pioneer, Onkyo, Denon, Yamaha, etc.) do not make very good speakers.
-Size matters. If you get smaller satellites, despite what their marketing says, rarely do they sound as full, open, and deep as full sized speakers. If you have a smaller room or a wife who won't let you have full sized boxes, fine; but if you have a larger room, go with floorstanders or bookshelves.
-Get the biggest subwoofer you can afford, at least a 10" (or larger if you have a larger room). Yes, an 8 inch sub looks less conspicuous but I guarantee that it will chuff or clip once it is fed deep bassy sound. Keep in mind that a 12" sub can always be turned down for less bass with no side effects but an 8" sub cannot be turned up without muddy, chuffed, or clipped output.
-Unless you have a perfectly square or rectangular room with sidewalls, a soundbar will not effectively simulate a rear surround field. Separates are ALWAYS better than a single output solution.