The next solar high is predicted to be the spring of 2013, and we can expect average solar activity compared to previous solar activity highs. As always, electrical devices, satellites, power stations and wireless communications will be affected by the solar high.
Planet Nibiru was originally said to hit Earth in 2003, but after nothing happened, the date was moved to December 21st, 2012 in accordance to the end of one of the Mayan's long count cycles at the Winter Solstice in 2012. If planet Nibiru were indeed going to hit Earth in 2012, it would be extremely visible in the night sky and astronomers would have been tracking it's path for decades, the planet is not invisible, it simply does not exist.
A planetary alignment is not due for another few decades, there is no possibility of Earth crossing the Galactic Plane in 2012. Even if it did, the effects on Earth would be nominal.
A reversal in Earth's rotation is
impossible. Magnetic reversals take place about 350,000 - 400,000 years on average and we are not due for a reversal for at least another few millenia.
Nasa tracks all Near Earth Objects. 433 Eros, the second-largest Near Earth Object on record (size 13×13×33 km) will pass Earth by at a distance of 0.1790 astronomical units (26,778,019 km; 16,639,090 mi) on January 31st.
It has been theorized by some that when the Sun aligns with the super massive black hole in 2012 the forces of the galactic core will have an extreme effect on the suns solar flare activity, however; this is completely impossible, Sagittarius A would have to be at least 25,000 light years closer to have any effect on the Sun's solar activity. Yes, the Sun does align with the galactic core, however; this is an annual event and has not done anything yet, so...
The Earth has been around and kicking for the past 4 billion years, and all of the events would have to have occurred before and within shorter time periods than the last major extinction, which was 65 million years ago.