Gnerally, the very best SLI boards also have excellent onboard sound (SB Live, Audigy recently), and 2 gb ethernet ports, and usually tend to OC a bit higher than the standard NF4 boards, although there are exceptions of course...
As to if those features are worth an extra $100, well,,, to some, they are. (The Epox variants have a good reputation, as do the Jetway boards, and of course Asus, DFI, MSI, Abit..)
If not OCing, the MSI K8N-Neo4F that I am using currently has been a delight to work with, utterly stable at stock speeds, and completely issue free. (Venturing into overclocking, howevver, it does not seem to like any FSB above about 216 MHz, regardless of latest MB bios, mem ratios, timings, HTT multipliers, so if your friend is planning on overclocking, I'd not recommend it, but it is flawless from at stock speeds thru a 7% OC...a good deal for $89 retail)
I'd also avoid the Gigabyte NF4 variants, I've read lots of users suffering from stuttering sound, reboots, etc..