I'm doing a backup of my computers, for example Time Machine on iMac and some drag and drop on Windows. Know any good storage devices that are at least 500GB in capacity? I'd like to drag my stuff from My Documents, My Music, etc. as well as storing my GOG games onto my disk, so I don't have to redownload them. Any suggestions, tell me what you're using, stuff like that would be very appreciated. If I can connect it to my network with Gigabit Ethernet so I can store my stuff without lugging the disk with sneakernet, that would be even super. Thanks!

Well, the most logical solution would be an external hard drive. They cost a fair bit more than a standard drive, but they are designed to be external and portable. I don't think you can hook one directly to the network but you can certainly map it as a network drive within OS X or Windows just as you would a permanent drive.
EDIT: oh, one major caveat: OS X can only read from NTFS, it cannot write to it. For best results you will want the drive formatted in FAT32. FAT32 doesn't work with very large files, however, so if you have whole movies or whatever to back up you may need to create a separate NTFS or HFS+ partition on the drive.

some of those cute NAS systems could do the work

You gotta love Apple's support of common standards :-D

I can live with the partitioning (gparted FTW), but I'll need a pretty big drive. Do 1TB external drives at a reasonable price exist?

I'd hardly call NTFS a "common standard". Especially considering nearly every version of Windows that supports it seems to use a different version.

Depends what you call reasonable. I bought my Buffalo Drivestation 1TB ECO last year for 129€, a reasonable price at the time (I could by another for less than 100€ now). Only caveat on this model is there's no on/off switch so I have to keep it unplugged when I don't use it.

However, I did read somewhere that a device formatted in NTFS from Vista will make it difficult for files stored to be read on XP. Small files are mostly unaffected apparently, but large files can be partially/completely corrupted. If you're planning on downgrading from Vista to XP for any reason, you could run in to trouble.

I've had a very good experience with Western Digital USB external hard drives, they sell any kind of disk from 500 TB to 2 TB (mine is an old 250 GB)... I formatted it in NTFS because I use a cloning software to make a huge image of my partitions and I don't want to spread them on gazillion different files....
On the software side of things, you would need a folder synchronization tool, that is a program that backup the folder you need to backup autonomously (maybe with tasks) with no manual "drag&drop".... For this I use DirSync Directory Synchronizer, it's rock solid.

A cheap western digital 1TB external drive retails here for the equivelent of 950hkd and would probably do the job. The only problem with externals of that size is that they're rarely, if ever, bus powered so you need a mains outlet handy. Thats why my external drive is never hooked up.
If you need to access the contents on multiple computers then a Network Attached Storage device is probably the best way to go, no need for a specific computer to be on for it to share data

The one's with 2,5 inch (laptop) drives do come usb powered but the one's I have take 2 usb ports. They have less capacity, are more expensive (250gb ~ 70€) and are slower (5400rpm instead of 7400rpm). But one the other hand they are more portable, smaller, quieter, more durable and produce less heat/consume less electricity than their 3,5 inch couterparts.

Actually yeah, I meant to add something about the high capacity drives invariably being 3.5s and taking too much energy to run off USB alone.
I'm not sure I'd call 2.5 drives more durable, I've had more issues with them than with 3.5s
NAS example. You get that enclosure and add whatever drives you want to it. This kind of thing would come with a HTTP user interface much like modern routers do so you can set up stuff like access permissions and the like

Thanks, guys. I looked at some drives online and I'm interested in a 500GB Maxtor. The WDs are nice, but a little too pricey. Since it's only 500GB, I'll have to deal with the iMac's Tme Machine some other way.

Time machine is basically an image program isn't it? Makes a full copy of the entire drive and stores it elsewhere to unpack in case there's a problem?
Can they be compressed at all? How big is the mac drive you have to back up?
Edit: From what I've just read on it, am I right in thinking the problem is that time machine needs the HFS+ format to store data? Couldn't you just partition the drive into an NTFS half and HFS+ half?