This article contains 3 very well done charts. There is no way of knowing if history is any guide at all to the future, but it is pretty much the only thing we really have to look at. Based on the P/E ratio, we MIGHT be either just at, or close to a bottom in the market.
The consumer spending chart would indicate that we are still at pretty high levels of spending relative to savings and will likely need to do some more catchup before we "return to the mean".
The housing chart is the most depressing of the 3 -- Fannie, Freddie and the Democrats took us a LONG way up a steep bubble and we likely to have to drop another 30-40% before we are close to returning to THAT mean.