A few BlackBerry 9000 styled themes have been floating around the net (some pretty good premium ones and some so-so freebies), but I can definitely say the just-released 9000s series of themes by Visto Themes is the best execution I have seen to date.
As you can tell from the screenshots, a ton of effort has been put into getting each and every detail just right. The 9000s theme is available in Icon, Today, Zen, Bottom Zen and L styles for most devices at a cost of $7. Keep in mind if you are running OS4.5 beta you could run into glitches with the Bottom Zen and L styles so you may want to stick to the standard layouts. Visto Themes offers excellent support, so if you run into any glitches you can always contact Corey.
Until the BlackBerry Bold is released this is arguably the next best thing!