Universe Today is reporting that an SUV-sized asteroid will pass by the Earth tomorrow at a distance of about 45,500 km (28,000 miles). That's close, but quite safe! The Earth is about 13,000 km (8000 miles) in diameter, for comparison. The rock will pass around the same height above the Earth's surface as orbiting weather and communication satellites.
The danger from this asteroid is, for all intents and purposes, essentially zero. The orbit has been nailed down enough to know it won't hit us (and even if it did, it would almost certainly not reach the ground; rocks that size make it down very rarely, instead exploding high in the atmosphere), and the odds of it hitting a satellite are roughly similar to two dust motes randomly colliding inside a football stadium.
The asteroid, named 2010 TD54, was discovered on Saturday, and will make its closest approach at 11:25 UT (07:25 Eastern US time). It would be a very tough observation for amateur astronomers, though not out of the question. It'll briefly reach about magnitude 14, within easy reach of a small telescope with a good camera, but it'll be screaming across the sky at high speed, making it a very rapidly moving target. If anyone can get images or video of it, please let me know!
This rock is interesting. The orbit takes it from 100 million km (60 million miles) from the Sun out to about 430 million km (250 million miles). That means it crosses the orbits of Venus, Earth, and Mars*! Not only that, the orbit is not tilted by very much compared to Earth's (about 5°), meaning it passes those three planets fairly often -- it orbits the Sun roughly every 2.5 years. I suspect this object hasn't been in this orbit very long. If it had been, it would've long ago smacked into a planet. If I had to guess, I'd say in the past it was on a different orbit and got nudged into this one by a gravitational interaction with a planet fairly recently. You can look at the orbit as well on the JPL Near Earth Object browser.
Given its odd orbit and the fact that it'll make such a close pass, I hope some big telescopes get good data on this flyby. I'm very curious about the origins of this little rock!
[Update (Oct 11, 13:30 Mountain time): A little more info can be found at >the JPL Asteroid Watch site.]
* To be fair, it doesn't get all that close to Mars, but it does get close to Venus, and obviously the Earth!