When is the new 5D coming?
Some people will tell you that it will be at Photokina in september (which is possible), some will tell you that it is urgently needed to beat Nikon and is just around the corner (also possible, but unlikely before Photokina, imo).
The reality is that people have been saying it is "just around the corner" for at least two years now, putting people off buying the current one as they will be better off if they wait.
There will be a replacement at some point (probably) but it still has no direct competitor at it's current price point. It still produces fantastic quality images and is also still selling strongly. So (despite what some will say) it isn't the creaking, aging monolith that is limping along in need of urgent replacement.
Until an official announcement is made by Canon themselves, any replacement date that people put forward is mere speculation and is no more valid than any guess you might make yourself.
My guess would be september at earliest (Photokina), probably 2009 though with PMA in march being a good candidate. This guess has no more validity than anybody elses though.
Price drop for original 5D?
Very little, if anything. The 1D/Ds IIs didn't plummet with the release of the 1D/Ds IIIs, the 30D hardly dropped when the 40D came out.
You have to remember that the 5D has already dropped in price dramatically. It's replacement will be at a higher price point and so there won't be a big need to drop the 5D further in order to clear old stock. There are still a lot of people who want the current 5D, many no doubt still saving for it, announcement of a new model may push many of these to get their orders in, before the old one sells out.
If you want one, waiting is only meaning that you are missing out on shooting with one of the greatest cameras Canon have produced. I know one guy who is constantly saying that he is going to get a 5D, he has been saying this since he tried mine 18 months ago. However, he keeps putting it off because he keeps being told that he should wait "as the new one is due out". He now really wishes that he had bought one 18 months ago, but still waits because it is now "so old" that the new one "must" now be just around the corner.