I think cloning is handiest if you need to copy the OS as well (so that you can copy it back, with all settings and programs ready to go without a need to configure anything).
If you just need a copy of the data, and you're proficient enough to format/reinstall/reconfigure your OS and programs, you can save some time by just backing up the data files (critical files). I do it that way - the "dumb" way - I just copy the data files to an external medium.
I do clone my OS - but only after a clean reformat with no data on it, and with all patches and everything configured the way I want it to be - so it's pretty small and tidy.
You have a lot of options. You can use alternate media like CD-R, DVD+/-R, external HD, another internal HD (I used to suggest flash drives, but some other forum members think they may be unreliable, so I don't know anymore). Like you said you can also used networked solutions. Network attached storage could work (I know nothing about those at all). You could also as you suggested set up a backup computer to use as a server, but I also wouldn't know how to set that up - just ask around the forum (separate thread would be good).
RAID 1 (mirroring) is good if you know what you're doing. A couple of words about that: you need a RAID 1 controller (some motherboards have SATA configured so that you can set it up to run as RAID 0 or 1). Then you just follow instructions in the manual to add the additional drive and populate it with the data either in the BIOS or in Windows... not sure how it's done. Ideally, if one of the drive fails, you should get an alert, and the other one will take over. Now here's a bit of advice: although it's recommended to use drive of the same geometry (size and physical layout (sectors, tracks, cylinders)), people will like to buy two drives at once of the same brand. No problem there, but I would advise buying them from different locations. Here's why: defective drives tend to come in the same batch. If you mix and match, the odds of both drives failing at once decreases tremendously.
See this article http://lwn.net/Articles/237924/
(6th paragraph down).
P.S: If you turn to optical media (CD/DVD), read this article:
You may want to use reliable media, check the data is readable from such media on a regular basis, and if you're really afraid, use multiple media (one copy on DVD+R, another on DVD-R - that's how I do it).