OK.
I just went through this. I have dickered around with mouting various sights on my SAR-1 in various configurations and positions. I'll try to sum up what I have learned in one brief post.
Mount
There are pretty much four options for slapping a red dot on an AK.
1. Mount that replaces the facotry rear sight. I didn't do this, since I like having the irons as backups.
2. Dustcover mount. Don't.
3. Combloc side rail. This is the "proper" way to do it, and it has the advantage of being designed for the weapon. The receiver can flex, though, and some mounts don't lock up very tightly, so maintaining zero can be hit or miss. You also have the choice of having the sight sit very high or very very high, or off to the left. And if you go with the "very high" option above, you can get pretty tight clearance for the dustcover, which can make cleaning slightly harder (big deal) and malfunction manipulations more difficult (more important). I tried the combloc mount and did not like it.
4. Ultimak rail or functional equivalent, putting the sight on the gas tube or immediately above it. I consider this to tbe the best option. It's out of the way, down as low as you can get it, and works very well with a red dot. The disadvantages are that ultimak mounts are not cheap, and you're putting the weight of the optic on the nose of the gun.
Sight
If money is no object, an Aimpoint on a low ring on the Ultimak is the way to go, period. Nothing is as rugged, dependable, and elegantly simple. You can use the dot with good cheekweld, and if the dot goes down you can look through the sight and use your irons. An Aimpoint Comp2 is what I had on my SAR for a while, and the setup just plain works.
If money is enough of an object that a used aimpoint is not an option, you have a couple of other decent choices. Any 30mm tube sight will work on a low ring, and most of them will allow you to look through the sight to use the irons. The S.P.O.T III sight is a "no name" sight that has gotten great reviews on arfcom that would work. Burris has a version of the same sight that would work as well.
Eotechs and other 'reflex' style sights will sit high enough that they will block the irons and may require cheek pieces if you like having cheekweld and not jaw weld. If you put them on a QD mount you will solve the problem of the blocked irons, but make the sight sit even higher. I had an OKO Holosight that I tried to use on the Ultimak and just could not get it to work right.
Russian Optics
Another good option are Russian sights. The PK-23 and the PK-A both have versions that will mount on the Ultimak rail in a 30mm ring. I have a PK-23 that I just got on mine right now and my only complaint is that the stupid thing juuuuuuuuust blocks the irons. If I have to switch to iron sights I'll have to dump the optic, or I may be able to crank up the FSP and the rear sight base and try running it like that. I'll lose my elevation adjustment on the rear sight, but, well, who uses elevation adjustments on AK BUIS anyway?
Mike
PS The reasons I moved the Aimpoint off of the rifle were that it seemed weird having an optic that cost more than the whole rifle on my beater blaster, and I had another use for the Aimpoint.
PPS Oh, I forgot. There is the Beryl rail and the copy made by Krebs. It basically puts the sights over the duscover but on a stable mount. Never used one, but the look very nice.