Wihtout looking at all those links, if you mean just an empty case, then forget about lights and chrome and artwork. Those things do not make a computer perform better. Get one with as many case fans as possible for good air flow and room for more if possible. Fans are a couple bucks each and well worth it.

If those links are for complete systems, then some general guidelines are:

If Windows Vista or 7: 64 bit version and 8GB RAM both vista and 7's features are resource hogs. You really want minimum 8GB RAM to use and enjoy all of them. If you've got WinXP just stick with the 32 bit version and 4GB RAM. But, upgrade to Vista or 7 when you can and min 8GB, it's worth it.

Vid Card: For gaming: my personal preference is nVidia as opposed to ATi. The current GT_ 2xx series with minimum 512MB [more is always better] vid memory.
For everyday use : if you're just checking email, watching youtube, or doing a spread sheet, any less-than-$50.00 vid card will do with minimum of 128MB vid memory.

HDD capacity isn't a big deal unless you're gonna be doing some major movie editing or just like to download lots of huge files for whatever reason. 100GB - 200GB will be more than sufficient. I am an avid gamer [at least 5 hours a day CoD WaW, CoH, Steam stuff, EVE Online, etc] and only have a 130-ish GB HDD with about 40% still empty.

unless you HAVE to watch Blue Ray movies on your computer, then any CD/DVD drive will do. Since Blu Ray capable DVD drives are so expensive, hell come up with another $150.00 and get a PS3 console system.

As far as CD/DVD and HDD goes, if you can, make sure they're SATA and not older EIDE. No, you won't really notice the difference usually, but SATA is current generation and faster.

power supply: really don't go below 500w rating. for gaming make sure the 12v "rail" has at least 25a output on it. The newer generation vid cards need it for they fans to turn fast enough to keep them cool.

Hope this helps.