Going by what you said, these tips should help you.
General rule:
-Use Newegg as a basis for price and user reviews. Their service is unparalled and the reviews provide great insight for some items. For example, I learned that my mobo doesn't work with OCZ memory so I knew I had to go with Corsair.
-Get cases from a B&M store or from an online retailer who gives you free shipping (ZipZoomFly is great for cases).
Motherboard: ASUS is generally a good starter mobo from what I've read. I'm fairly happy with my ASUS mobo. There really aren't any mobos that are... laid out very poorly. If it is, you can usally find out what's wrong with it in the user reviews.
Case: The case is usually what leads to the most headache when putting things together... some cases are very poorly designed. Try to go for a mid-tower case so that you have room to work with. A full tower would be better but they're overkill in most cases (pun!).
Graphics card: it doesn't matter what mobo you get, the GPU isn't very picky as to what mobo you use as long as you get one that'll fit in your mobo.
SLI: any nForce mobo with 2x PCI-e slots will be ready for SLI.
nForce: NF4 mobos are cheaper and generally offer 2 PATA (aka IDE) ports whereas NF5 mobos offer one PATA. The reason I list that is because PATAs take a performance hit if there are more than two devices on the same port being used at the same time (for example, an optical drive and a HD.. they share one line so they're both limited). Another difference between NF4 and NF5 is that NF5 has better memory management, which is essential for an AMD system. A higher NF5 number means its better overall... NF550 is basic, NF570 is mainstream, and NF590 is enthusiast. I think an NF570 mobo will be best for you.
Processor: while you do save money by going with an A64, the multitasking capabilities of a dual core processor are very nice.