What is the Different Between Slim and No Slim (xbox 360)?

I found BOX SLIM 360 250GB CONSOLE 250 GB selling on ebay.com and the price low than the Xbox 360 250 GB Console I found on Microsoft.com

So what is the different of them?
Please help me, I never use xbox 360 before, I'm new on this stuff but I want to get the right one.
Thank you.

Suggestion:

I hope this would help you to know more about the Xbox 360. In my opinion, The Xbox 360 has some new features then old 360 don't have.

Best Selling XBox 360 Console Bundle:

http://www.amazon.com/Xbox-360-250GB-Reach-Console-Bundle/dp/B003O6EETU/ref=sr_1_1?s=videogames&ie=UTF8&qid=1285325717&sr=1-1&tag=bilo-20

Features and Design
• Excellent online service, packed with features
• More reasonable price
• Glossy black casing
• Good price point
• The buttons are touch sensitive and require no pressure.
• Built in WiFi – New Xbox 360 supports 802.11 b/g/n wifi
• Five USB ports (two on the front and three on the back)
• AUX port specifically for Microsoft’s Kinect motion device.
• It is much quieter and runs cooler.
• Aesthetically pleasing user-interface

Top 5 MUST have games right now in Xbox 360.
• Halo Reach
• Call of Duty: Black Ops
• Medal of Honor Limited Edition
• NBA 2K11
• Fable III

The Xbox 360 can also display pictures and perform slideshows of photo collections with various transition effects, and supports audio playback, with music player controls accessible through the Xbox 360 Guide button.

See here for a very good article from an actual owner, see how he says about XBox 360 latest bundle.

http://www.amazon.com/review/RHQI93UJJDMQ5/ref=cm_cr_pr_perm?ie=UTF8&ASIN=B003O6EETU&nodeID=&linkCode=&tag=bilo-20

Latest bestselling game list of XBox 360:
http://www.amazon.com/s/ref=nb_sb_noss?url=node%3D14220271&field-keywords=&x=0&y=0&tag=bilo-20