i5 is the best bang for the buck, and absolutely murders an AMD equivalent (also costs more for the same specs for Intel). Also, w/ Sandy Bridge, you'll get a large jump in battery life, if that makes a difference for you.
I used to be a huge AMD fan, but they haven't put anything out that can touch Intel in desktop, laptop, or server CPU's in several years (that's not me talking, there are plenty of benchmarks to back this up).
That being said... $500 is a low end laptop, but I found a Lenovo G570 on newegg w/ an i5 CPU, 4GB, 500GB HD for $549 w/ free shipping.
http://www.newegg.com/Product/Product.aspx?Item=N82E16834246309 - I have a Lenovo Thinkpad T410 and it's quite solid.
It does have integrated Intel HD graphics, which are not stellar, but have a good performance to power ratio, and should have no issue streaming Netflix HD content at all. Do some Google searches on i5 vs AMD equivalent, there really is no comparison.
Edit:
If you can spend a touch more - and graphics are of a concern - this is $100 more expensive, but has an 1GB NVIDIA GeForce GT630M, which is a good jump over the Intel HD graphics:
http://www.newegg.com/Product/Product.aspx?Item=N82E16834246327
Cheers.