The ECS supports 24GB RAM, the Intel supports 16GB. Along with that, the ECS supports the full 24GB in triple channel, while the Intel will only do 12GB in triple channel. The ECS supports Crossfire only, for ATI cards, the Intel supports both ATI's Crossfire and nVidia's SLI. Different RAID options (0/1/0+1, 5 on the ECS, 0/1/5/10 on the Intel), The ECS has two LAN ports, the Intel has one. The Intel has more compatible processors (it'll run most 1366 Xeons, if you want) the ECS is more limited. Probably some memory support in there for more options, you'll want to look at the QVL for both boards on their websites to figure out what matches.
Memory support for the Intel
http://www.intel.com/support/motherboar ... 029865.htm
Memory list for the ECS
http://download.ecsusa.com/dlfileecs/ma ... B-A%20(1.0
Of the two, the Intel is more server oriented, not really meant for overclocking, if you have any thoughts of doing that. Intel boards are typically very solid, dependable, and speedy as is, but you can't really push them too hard. The ECS is an older model, not made anymore, but it's geared toward the enthusiast that wants to push their overclock hard.
Pretty much take your pick. I might skip the ECS (depending on what your price is) and the Intel both, and get a newer, more up to date board designed around consumer use. Asus and Gigabyte are both quite good. There's a review of the ECS here in the review section...
http://www.motherboards.org/reviews/mot ... 843_1.html
Read over that, and see what you think.