1. That processor is significantly better than the Phenom II X2 550, BUT
It's just a Phenom II X4 955 with .2Ghz higher.
Save yourself the $20-30 and get the Phenom II X4 955 instead of the 965.
2. Yes several.
The Hard Drive:
The Samsung Spinpoint F3 outperforms the Seagate 7200.12 in read/write times.
You may purchase one here for the same price as the Seagate you selected.
SuperBiiz.com - Samsung HD502HJ 500GB SATA2 7200rpm 16MB Hard Drive
On Newegg the AOC 22" costs $160+17$ Shipping=177$ Total
You can get the same exact monitor on Buy.com for $150 with free shipping
AOC 2236Vw Widescreen LCD Monitor - 2236VW - Buy.com
ONLY and I mean ONLY get the 790X IF you plan on doing Crossfire in the future. (Crossfire does not work with Nvidia cards, such as that 9800 GT you selected, but I'll get to that in a moment.)
Otherwise you should get a 770 motherboard or the Asus 780L
The Truepower New 650w is OVERKILL for your system. You WILL NOT need that much power.
Newegg.com - OCZ ModXStream Pro OCZ500MXSP 500W ATX12V V2.2 / EPS12V SLI Certified CrossFire Ready 80 PLUS Certified Modular Active PFC Power Supply compatible with core i7 - Power Supplies
That PSU is cheaper by a LOT + it has a promo code so you can get 10% further off until the end of February, and it could power two graphics cards in crossfire quite easily should you ever choose to do that.
The 9800 GT is the best card you can get for $100, but if you clear up some money by cutting back the other things, you should be able to afford a BETTER graphics card.
(Note you can not SLI two 9800 GT's on a 790X motherboard.)
(790X motherboards are only if you want Multiple graphics cards setups, but can only do crossfire with ATI cards)
3. Compatibility Issues...
Nothing that I didn't already cover.