Speakers are a very subjective choice and there are a ton of different options out there. We can suggest good models to go out and audition and hear for yourself, but you'll have to give more info first, such as: -room dimensions (the size of the room has a big effect on what size speakers you need to fill it with sound) - budget - what type of music you like - what you are going to be using the speakers for (the ratio of music to movies/tv/gaming).
You will definitely notice a difference going to separates for your sound system instead of box sets, and you can get quite good sound for a reasonable price. In the speaker world, there are some speakers that offer fantastic value for the price, others that give you what you would expect for that price, and then some that perform poorly but cost you an arm and a leg to make you think you are getting great speakers (mainly BOSE, but there are others as well). We can help steer you to the first category to help you in your search.