I found this comparison fairly interesting, so I thought you guys might, too.

I took current total sales approximations for all systems from the current generation and last generation, then divided them by the number of months they've been out for (rounded to the half-month). Calculations are measured out to when their successor was released (if they are last gen), or in the case of the Dreamcast, it's rounded to when production ceased.

 These are solely approximations, and I didn't waste that much time putting them together, so don't bother checking for perfection. I just thought it was interesting, though, seeing how everything compares. 

DC - 0.38m

PS2 - 1.44m

GCN - 0.36m

Xbox - 0.41m

DS (both) - 1.4m

DS (lite only) - 1.7m

PSP - 0.76m

Xbox 360 - 0.51m

PS3 - 0.49m

Wii - 1.19m

Two things I found particularly interesting:

 (1) Dreamcast, while it was alive, sold at a better rate than the Gamecube. Would it have possibly done BETTER than the GCN, had SEGA continued production?

 (2) People claim that the Wii has a chance of passing PS2 in sales, but the current sales numbers disagree with that. Of course, sales could easily pick up (as PS2 sales followed similar trends within the first year after launch), but if trends follow current rates, Wii will likely be around 95m after a similar lifespan (giving 80 months between system launch and successor launch).

Do keep in mind the Wii sales are limited by supply for now. We can't know at the moment where the average will end up when supply catches up to demand.

The Gamecube didn't live much of a life past Q4 2005 and I suspect that its average monthly sales before that point were higher than the Dreamcast.

Umm...averaging together years worth of data is not going to yield a useful monthly average. Systems sell differently at different points in their lifespan.

Also keep in mind that the Wii has yet to experience a 'true' holiday. Same with the PS3.

You are ignoring some things here:

-The Gamecube was alive for a lot more time than Dreamcast, so its logic it has a lower average monthly sales figure.

-The Wii was released just 9 (9 right?) months ago, and the PS2 had its pike on monthly sales when it got really cheap... around $175 if I remember correctly, so is premature to state that the Wii can't reach the PS2 in sales, while it hasn't seen its first price cut yet.

-Don't forget that some people that got its PS2 to die, got a new one, and to my knowledge is a rather high amount, considering the total sales of the PS2... for example 10% would be around 12 millions.

Just wanted to point that out.

Those dead systems people had to replace have always been a point of contention for me. Some people say "well they probably got a few good years out of them" but to me thats just a really bad way of looking at it. Just for the record I have felt this way since well before this generation so it has nothing to do with any sales records..except maybe that if an honest accounting of PS2 sales were done its possible PS1 could still be the alltime seller.