From the top of my head there is vectorebike.com from germany.
They got a light weight one. http://www.vectorebike.com/bikes/the-vector-light.html
A "standard" 20s battery will work with most all controllers, and paired up with a powerful motor like I listed in previous post you will top out at about 60 mph if motor is laced into a 18" wheel. You can gain a little more top speed if you volt higher or up to 19" but that will come at a price. As a direct drive hub motor does not have any internal gearing, the only way to change gearing is by changing the rear wheel size. Now a 17" wheel will give you more torque and climb better and accelerate stronger then if you lace the same motor into a 19" wheel. You will loose some top speed, but on the other hand you will gain faster acceleration and torque so you can climb steeper hills without overheating.
Also volting higher then 20s can be tricky. Most of the commonly available controllers in the e-bike scene are made with internal hardware that can handle up to about 90v. The closer you run to that 90v the more risk of blowing a mos fet or causing damage to your controller.
Motors are pretty much happy with whatever you feed them. They don't care much. Higher voltage means higher RPM and higher top speed. But if going 24s or even higher you need to be certain you run a controller that can handle the voltage. Those kind of controllers are available so it is up to you to set your boundaries.
In general I think most people here on ES will agree, at least to some extent that more important then top speed is acceleration. Acceleration is what will put that grin on your face every time you twist that throttle. So as a first build I would recommend to stay with 20s battery and find a controller with high peak phase current. Preferable with torque throttle.
As with everything else, the more power you put into your ride the more you need to factor in that power when choosing other parts. Like brakes, rims, hubs. spokes, shocks and fork. Those parts will make sure your bike handles well and will keep you alive. Neither one of them is to be skimped on. I mean you don't need a 500 $ competition DH grade rim, it will be nice but you could choose a motorcycle rim for 50$ and still have the safety margin on your side. For brakes, well if you ride hard put some money into at least a good front brake. Remember it is not all about the number of pistons or the rotor size, those can be good indicators but you want stuff that works well too. Front brakes you need to modulate. You need a set that you can easily apply the right amount of pressure to in each situation. Cheapo chinese brakes don't work well.