Replacement mobo for asus a8n-e

If you can find one, I'd say this one by Foxconn:

http://www.xpcgear.com/nf4sk8aa8krs.html

But the fact of the matter is, it's going to be pretty difficult to find any DDR motherboard new. They don't really make them anymore. If you can part with the RAM and move up to DDR2, there are a ton of boards that ought to suit your needs. You could even get something like this and be able to upgrade your other components one-by-one as needed:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

It's probably going to be well worth it to get that one and go to DDR2 or DDR3, because it also sounds like most of your other components are 4-5 years old and should be replaced in the near future as well. I'd honestly say an entire new machine is the way to go, but if you're not ready to spend a few hundred dollars at once, that could let you do it gradually.

Also: There usually isn't a need for more than one DVD or CD drive, so even though this board only allows two IDE devices, you won't be giving up much.