Need advice $500 gaming rig

Hello All, new member here. I haven't built a system in 5+ years and I'm way overdue and overwhelmed by the new tech and options available. My current system is a Pentium 4 (socket 478) / GeForce 6200 if that gives you a hint where I'm coming from.   I recently reactivated my Warcraft account in preparation for Cataclysm, and can only play at the lowest video settings.

I've been reading these forums off and on the past few weeks, in preparation for buying new parts for a budget build. I'd like to keep the new purchase around $500, which will still give me a huge boost over my existing system. I basically want to make sure the parts I've selected below are compatible and a good value.

Approximate Purchase Date: Immediate.
Budget Range: ~$500
System Usage from Most to Least Important: Gaming, internet.
Parts Not Required: Monitor, keyboard, mouse, speakers.
Preferred Website(s) for Parts: Newegg
Country of Origin: U.S.
Parts Preferences: Intel, Asus.
Overclocking: prefer not to.
SLI or Crossfire: preferably not.
Monitor Resolution: basic 1024x768. I'm ok with that.  
Additional Comments: Just looking for something to improve my Warcraft experience. In a year or two I might revisit my options with a new build and pass this machine onto one of my sons, so I prefer a budget build at this time.

Here's what I'm looking at so far:

CPU (i3-550) $110
]http://www.newegg.com/Product/Product.aspx?Item=N82E16819115065]
Comment: I know I can probably do better with AMD dollar-wise, but I'm old school Intel since my first 486 almost 20 years ago.

Mobo (Asus) ~$105
P7H55 ]http://www.newegg.com/Product/Product.aspx?Item=N82E16813131662]
P7P55D-E ]http://www.newegg.com/Product/Product.aspx?Item=N82E16813131634]
Comment: I'm at a loss as to the differences and which is the better between these two. Your thoughts?

GPU (ASUS ENGTX460) $130
]http://www.newegg.com/Product/Product.aspx?Item=N82E16814121390]
Comment: Decided on this card based upon the forums here, I'm an Asus fan, and it's a good bang for the buck. Not comfortable with SLI or Xfire builds, so hoping this single card will do the trick.

RAM (G.SKILL) $50
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231277&cm_re=G.SKILL_Ripjaws_Series_4GB-_-20-231-277-_-Product
Comment: wide open to suggestions on the best ram for this system.

HDD (Barracuda) $50
]http://www.newegg.com/Product/Product.aspx?Item=N82E16822148433]

Case
Comment: My current case has a 420w Raidmax PSU, I'm concerned whether this is good enough for this proposed system, or if I need to upgrade. I'm also concerned about cooling, so getting a Cool Master case isn't out of the question.

Thanks for any feedback and suggestions!