Sound design is a bit of a generic term. I'm assuming your looking for something focused on design for film. There is a sound design news group that is mostly film though some games also. Look in Yahoo groups for SOUND_DESIGN.
You could also look at the DUC in the post section. You can at times find interesting info on mixer oriented boards such as the CAS board and JW's site. There are a number of sites that deal with Foley and FX and some have boards. As a general kind of thing sound design lists are not all that useful, interesting I have found. There is a lot of "how do I get great lightsaber sounds", or discussions on how to use a sampler to do Foley. On the one hand some is interesting but it gets pretty repetitive and a lot of questions are asked by folks who are very green and very into trying to create everything in the computer. I use the computer a LOT but I find this desire to create things that are easier to record a big problem and one of the reasons a lot of big money projects have some very uninteresting sound. So I tend to get pissed if I spend too much time reading posts about how to create car bys from scratch.
The DUC is more nut's and bolts post but a good place to ask questions about how to do something. There are a lot of working pro's that visit and you can get some really good info.