Intel--Very stable, can't be beat. Here, buy a board based on the i845D for DDR, or if you can afford it, the i850E which uses RDRAM--this supports the latest PC1066RDRAM.
Via--I haven't had problems with them, but they are notorious for being unstable. The latest chipset on the AMD side of things is the KT333, but the KT400 is right behind it. On the P4 side of things the P4X266A is available and the P4X333 is on the way. Intel has a bit of a beef with Via over a liscensing issue, so not many companies have jumped on the Via P4 chipset bandwagon.
nVidia--Only for AMD. These are very stable, highly integrated chipsets. If you go the AMD route, I would definitely be looking into this chipset. Go with either the nForce 420 or 415---I suggest the 415 as it lacks the integrated graphics, which is good if you plan on using an external graphics card anyway. I use Abit's NV7-133R in my main box and it's a wonderful board (plug:chk: )
Sis--They have some chipsets for both AMD and Intel. On the Intel side the newest is the SiS645 which features DDR 333 support, and is officially sanctioned by Intel. A newer, and faster version of the chipset, the 645DX would be better to look into as it should future-proof your investment a little longer. On the AMD side, the 745 is the latest, but hasn't been really hot in the motherboard market. ECS is big into Sis, but I really don't like their boards--mainly because they seem to be finicky about what cards you put in them.
ALi--I don't really know much about their chipsets. I do know they have a P4 chipset out, but the only company I recall using it is Iwill. Same for their Magik 333 Athlon chipset, and the board using it is the Iwill XP-333--which I've heard is very good.
Basically, these are the options. Now let me throw out some questions for you: Do you have a preference to Intel or AMD? What is the price range you are looking at to spend on a new motherboard? What features do you want on this motherboard?