They have all sorts of fancy flatscreens they're working on for better inside visibility, feeding you images from cameras located around the vehicle. They're also working on remotely operated turrets so a crewman doesn't have to poke his head out to use the pintle mount. But for all that, the visibility still sucks.
I can't find any good examples on the web for what the interior of a tank looks like. Old-style tanks had view slits, deliberately kept small so stray rounds couldn't make it through and so nobody could chuck a grenade in. Modern tanks use armored glass over the slits as well as periscopes.
The best visibility solution I've seen theorized is still from scifi. You have a curved screen extending through a 270 degree arc with the image blended in realtime from multiple cameras around the tank. The image is slightly compressed because it shows the full 360 degrees surrounding the tank, thus giving the commander the ability to look everywhere at once. Someone walking behind the tank would walk off the left side of the screen and onto the right. The orientation of the screen could also be turned so if the commander wanted to have the view centered on something direclty behind, the "gap" would now occur at the front of the tank. When combined with a head-mounted targeting system so that the gun can slew to where the commander is looking (already exists on modern attack choppers) the commander would be able to engage targets as soon as he sees them.
The next step would be cutting down on the number of crew in a tank. Right now the Abrams requires a driver, loader, gunner, and commander. Some modern tanks have made use of an autoloader but the US Army has traditionally not trusted them. The Stryker's autoloader is troublesome. Assuming you can lick that target, that's one crewman down. The next question is one of multitasking. In a modern tank, driving, shooting, and directing the tank are seen as three different jobs that require the dedicated attention of a crewman. In modern combat choppers, flying is seen as complicated enough without trying to shoot as well so the second crewman is a dedicated gunner. That same divison of labor is seen in some combat aircraft with a backseater required to operate the additional systems the pilot does not have time to mess with. The Commanche managed to do away with the gunner, the pilot operating all of the aircraft's equipment. The Raptor does not require a backseater. I can't really see a tank getting down to less than two crewmen since the tank can move and shoot in different directions, you have to have someone driving it when the gunner is looking somewhere else.