What should I look for in a digital camera?

I'm trying to buy a new camera for ebay use. I bought a Mitsuba DC500T 12.0 Megapixel camera a year ago for $172 off of an ebay auction, it was fine for taking pictures of larger things at the time, but its worthless for getting detailed close up pictures!

So I'm willing to spend in the $500-600ish range for quality and thought I'd ask someone with photography experience, their opinion on these or other cameras?

http://www.crutchfield.com/p_054D3100/Nikon-D3100-Kit.html

http://www.sears.com/shc/s/p_10153_12605_00338524000P?prdNo=2&blockNo=2&blockType=L2

http://www.sears.com/shc/s/p_10153_12605_00352973000P?prdNo=9&blockNo=9&blockType=L9

I buy and resell broken Ipods on ebay ( cnelson1985 ), and need a camera that can zero in on the scratches ect.without the blur, so I don't need one to take distance pictures, but one that would be good for close up detail.

Added (1). Yeah, but the problem with ebay is alot of low quality stuff thats souped up to sound great or overpriced.

Ebay.com lol they have everything

Yes this one is good Nikon D3100 14.2MP Digital SLR Camera
* 14.2-megapixel DX-format CMOS image sensor;
* 3-inch monitor with One-Touch Live View shooting and movie capture
* Full 1080p HD Cinematic Video with full-time autofocus and sound
* Easy-To-Use Nikon Guide Mode with intuitive controls and on-board assistance
http://www.amazon.com/...003ZYF3LO/
http://rover.ebay.com/...m270.l1313