The 600T is a great case for cable management, with its grommeted cutouts and capacious behind the tray area, so it's easy to do a solid job with what I'll call "practical" cable management. That is, cable management that gives you the practical advantages of unrestricted airflow and less tangled mess in your PC internals, but likely isn't particularly concerned with aesthetics. The purpose of this how-to is to give 600T owners an idea of how to knock things up a notch from mere practicality. Our goal is to arrange our internals in such a way that all the practical benefits of cable management are retained, while simultaneously achieving a "clean" internal aesthetic (one that will look great when viewed through your case window, 600T SE owners!). This isn't exhaustive or definitive, there are loads of modifications that you can do (with or without tools) that can help you achieve an aesthetically pleasing PC (internally and externally). I'm going to focus mainly on some very basic concepts that can help with getting a "clean" look.
Every clean build starts with cable management, so below are some rules, tips, tricks, etc. that should assist in really nailing that part of your build.
Make sure you've got the right tools for the job. Grab a lot of zip-ties (I prefer black), enough to tie down your cables 2 or 3 times over. Trust me, you'll be changing or moving or adding cables to various bundles behind the tray, and you don't want to run out of zip-ties. Also pick up some side-cutting pliers. Many pairs of needle-nosed pliers have side cutting blades as well, but I prefer a pair with just blades for cabling work, they're easier to use overall. If you like, you can pick up a few cable tie-down dealies, but I've found those already present in the 600T to be adequate.
Minimize visibility of cables coming from the PSU. Pull those cables all the way through the grommet, don't leave any extra cables or slack hanging around there. If you have a non-modular PSU and can't fit everything behind the tray, get the cables bound up tightly. Keep the bundle near the back of the supply, but not directly on the PSU vent (if it has one there).
Try to keep those cables away from empty spaces in the motherboard tray. Your objective is always to minimize the visibility of cables, even if they're completely out of the way of airflow.
Minimize the slack in your cables as they come out from behind the motherboard tray. So, if it takes 4 inches of cable to reach whatever socket it's powering, you should see only 4 inches, not 6. Once again, we should see as little of the cables as possible. Don't worry if the cable has to make a pretty sharp turn to make it into the socket, cables in quality PSUs have good, thick wires that can handle serious abuse, so a couple of bends are not a big deal.
Buy SATA cables of the length you need. So an 18'' cable is probably most appropriate for your optical drive, but you can likely get away with a 12'', 10'' or shorter SATA cable to your storage drive(s) depending on positioning. This isn't a huge deal, but it can help keep cable clutter down just a bit, as you won't have a lot of extra slack to bind up and keep out of the way.
If you'd like to take your cabling up another level, you can invest in sleeved extensions. These are special cable extensions where the individual wires are single-sleeved and heatshrinked into the sockets. This can provide a particularly good looking cabling job, but you'll have to deal with the additional length provided by the extensions.
If you [i]really[/i] want to kick things up a notch, you can sleeve your PSU. If your PSU has hardwired cables, you'll have to void the warranty to accomplish this. If you have a fully modular PSU, and can obtain a spare set of cables, you can have a set available (should you have to RMA the supply) and an extra set to sleeve. Some online stores offer sleeving services, and PC related forums with strong modding communities sometimes have members who will sleeve your PSU for a fee. Alternately, you can purchase the sleeving material and heatshrink and do the job yourself. It's time consuming and tedious, apparently, but if you do it right the results are hard to argue with.
Also consider some other steps. If you're only running 3 drives, take out one of the cages. If you're up for it, you can take the front cover of the case off and remove the stand that the drive cages are mounted on. You won't be able to have drives there, but if you only need 1 cage you can just move it to the designated spot next to the PSU. Consider forgoing an internal optical drive, instead use an external drive. It's easier to use (mine sits closer to me, right on my desk) and makes the PC look a bit better. Alternately, you can buy a drive cage that fits in your 5.25 inch bays, and have your internal optical drive paired right above your drives, completely clearing the floor of the case, and (depending on the drive cage you use) giving you a 120mm fan in some of your optical bays.
As I mentioned at the beginning, this isn't meant to be a definitive look at what to do with your 600T. Still, putting some of the basic steps here into practice can give you an idea of what a little time and elbow grease can accomplish, even without lots of modification to the original case. And, really, if you're spending ~$150 on a PC case, I feel like you should definitely put some effort into the "looks" side of things.