I only see an Asrock board on Newegg with the ULi 1695. It probably has minor overclocking but they haven't been known for more than that.
I do see some ULi 1689 boards such as the Gigabyte GA-K8U. Their web site claims overclocking features. I almost got one, but ended up with a Chaintech VNF3 board for $55 shiped.
The major companies do make some innovations. Asus/Abit were among the first that had PAT-like abilities with 865PE chipset, and among the first to hit higher than 10% FSB clocks on the newer Intel 9XX series chipsets. Gigabyte spearheaded a redundant BIOS. MSI... what did MSI do? Er, perhaps make red a popular PCB color?
As for "alternative" chipsets the top manufacturers do use those chips. Gigabyte already has the lower end ULi chipset on a board. MSI and ECS makes ATI chipset boards. Asus is well known for their SiS chipset boards. I have a few P4S800-MX boards that work great with the mobile CPUs. P4S800 was a good overclocker with all the voltages and such for a low price. The Asus SiS 655 chipset boards (forgot model #s) were known to be budget alternatives to the 865PE chipset overclocker boards, with full FSB/voltage and AGP lock, with performance and overclockabilty like the Intel chipset boards.
The other part of the story is what sells. Just ask around here, "what socket 939 mobo do you recommend" and everyone will chime in with their favorite Nforce4 chipset board. Is it because there are no good alternatives to recommend or is it because people would recommend Nforce4 anyways? Chicken & egg problem. Manufacturers want boards to sell. They know that if they make two otherwise identical boards, but one of them uses Nforce4 chipset, that one will outsell the other.