look at my signature link to build. i have an all in one receiver+speaker setup that does just that.
you have three options generally if you want 5.1:
-speakers with multiple inputs like the z906 however since they only have two inputs you will be swapping inputs alot to make it work nicely or using many adapters and switches which is ugly and a pain. you could use normal pc speakers like the z506 but would need an adapter to handle the digital optical inputs (see below note on two speaker option)
- htib setup which while cheap (and you need to be careful that they actually have inputs for 5.1 aux audio inputs!!! many do NOT and are stereo input!). your amount of inputs and type is going to be limited just like above though. (not suggested, you will wish you had not later)
or...
-receiver + speakers + sub. you have plenty of inputs and can run everything with a simple knob turn or button push. while certainly a more expensive option it really is well worthwhile if you want 5.1. they do make 2.0 models as well if you dont need the speakers but honestly its worth using a 5.1 for the future upgradability.
monoprice 10565/energy 5.1 take are cheap speaker+sub sets that sound good and you can get a sony or onkyo receiver for under $200. for under $500 you can get a great intoductory system that you will have for years.
of course you could always go the powered speaker route and just use two powered bookshelf speakers (analog input) and use a switch box to control inputs if you wanted to stay cheaper, did not need 5.1, did not need a subwoofer and wanted to keep things small and easy to move around.
things like the mackie cr3/cr4, m-audio av30/av40, krk-rockit 5, etc would work if you have a small setup where you dont need excessive power. for inputs that are digital, you would need a decoder (likely you would use optical to 3.5mm audio extractor). while this falls into the multiple boxes syndrome if your devices are many its cheaper than a receiver IF you dont need 5.1 (5.1 with such boxes is just messy, higher priced and a pain)
not all soundbars are garbage, some actually sound half decent. most are similar to stereo sound though so you can put them in the same class as the above two speaker option. limited inputs, but you could potentially use one.