OK, at newegg, I have priced out 2 systems:
System 1 is based on the Gigabyte GA-EP43-DS3L and comes to(557.91)

System 2 is based on the Intel BOXDP43TF and comes to ($572.91)

Both of them include these components (which I believe are compatible):
Rosewill R220-P-BK BlackATX Mid Tower Case - Retail
Rosewill RP550V2-S-SL 550W ATX12V v2.01 SLI Ready Power Supply - Retail
Intel Core 2 Duo E8400 Wolfdale 3.0GHz LGA 775 65W - Retail
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel
Western Digital Caviar SE16 640GB 7200 RPM SATA 3.0Gb/s Hard Drive - OEM
Pioneer 20X DVD±R DVD Burner Black IDE - OEM
MSI RX2600Pro-T2D256E Radeon HD 2600PRO 256MB 128-bit GDDR2 PCI Express x16 HDCP Ready Video Card - Retail
ARCTIC COOLING Freezer 7 Pro 92mm CPU Cooler - Retail

Is one of these boards better than the other? Is all of this compatible with OSX? And are these components ok to work together or are they junk?

The EP43-DS3L can overclock and works in OS X, so I would go for that. Both are good boards though. Not sure if the Intel board works...but it should!

Anyway, I would go for the Gigabyte.

Cool. I'm leaning that way myself. The Intel board has one entry in the 10.5.2 HCL. Says everything worked OOB except LAN and Audio, but has kexts for those.

Is G.Skill memory ok or should I spring for Corsair or something else? And that cooler was highly rated, but is there a better one for around 20-30 bucks?

The cooler is a bit noisy + overkill in my opinion. I like the Zalman range - effiecient + quiet.

G.Skill is cool.