On Wednesday morning/afternoon, the Moon will appear to pass directly in front of Venus for people in North America.
This kind of thing is called an occultation, and it doesn't happen very often, so you should take the chance to watch. It won't be easy! Since it happens in broad daylight, Venus will be hard to find. So will the Moon: it'll be a thin crescent, just a few days before new.
The lunar-occultations website has a map of viewability and a table with times for big cities in the US (Boulder's not listed, grumble grumble, but Denver is close enough). For me, the Moon's disk will slip in front of Venus at about 1:25 local time, and Venus will reappear at 2:06. The Moon will be about 23 degrees above the horizon, so it'll clear the mountain range to my west. If it's not cloudy, I'll have a decent shot at seeing this.
Again, though, it's not easy. The table linked gives the azimuth of the event as well, the direction to face. 0 is north, 90 east, 180 south, and 270 west. For me, it'll be at an azimuth of 224 degrees, or southwest. So I'll face southwest, and look about 24 degree up (roughly, twice the width of your outstretched fist). I'll be using binoculars at least at first; that'll make the Moon and Venus easier to see, and then I'll test my eyes and look for it unaided. You can see pictures of an occultation from 2007 at the popastro site.
The actual event is pretty cool; the Moon and Venus will appear to get closer and closer, and then bloop! Venus will disappear. Since Venus is actually a disk, and not a point source, it'll actually take a brief moment for it to disappear; it's not all at once. It depends on the phases of the Moon and Venus, and the position on the disk of the Moon where Venus gets occulted (if it's near the middle the event is quicker, near the poles and it takes longer). It should take somewhere between 20 seconds and a minute, if I've done my math right.
So go out and take a look! Hat tip to Amanda for announcing this.