If you’re really short on space and want a soundbar to sit in front of your TV, you’re going to have to go for something really slim and low profile, like the LG 3530a, which will slot right underneath without blocking your TV's picture or infrared sensor.
If it does sit any higher than this, make sure it features an IR repeater, which will pass through your remote control's signal to your TV.
Due to their slim stature, a lot of soundbars like this will come with a wired or wireless sub. You can experiment with placement but we’d always suggest keeping it as close to the rack as possible for the most cohesive sound – something to consider as the subs can vary in size too.
On the other hand, if you have room for a bigger soundbar, then consider something like the Monitor Audio ASB-2. Combine bigger drivers with its bigger cabinet and you may not find the need for a separate sub at all, though you will need to check your rack is wide enough to fit it, or consider wall mounting it instead. Still want more low end? The ASB-2 does have a sub out for adding one if you wish, but doesn't come with one included.
Finally, it’s worth keeping an eye out for shape-shifting soundbars like the Philips HTL9100.
With this one, you can have it set up in a normal design, but it also has the flexibility to remove the ends and make them into rear speakers if your room will allow. Clever stuff.