Some real features on an iMac you can actually brag about beyond its price tag:

• IPS panel across all model and sizes, giving you superb viewing angle and color gamut range (most panels should be from LG.Display)
• Depending on the iMac generation you're getting, you'll be sporting a fairly decent GPU, from the low/mid-range Radeon HD 4670, to the 5670, and finally to the current mid/high-end generation of 6770M to 6970M.
• Optional SSD available on high-end latest generation iMac. 
• Thunderbolt port so you can buy yet another cable or adapter :)