IMB - My family and I served with the International Mission Board (SBC) while we were in South Asia. What I like best about the IMB is the emphasis on church-planting. The goal is rapidly-reproducing local house churches, which are led by national pastors. This model has the potential to reach millions of people because it does not rely on outside financial investment or buildings.
Joshua Project - This site is an excellent source for all kinds of information about unreached people groups. It is stunning to think about the fact that 42% of the people groups in the world remain unreached. If you have a blog or other type of webpage, consider posting the "Unreached People of the Day."
Matthias Media - At this location, you can find one of the best tracts that I have seen. Why is it good? Because it begins with God, not man.
New Tribes Mission - NTM is a missions-sending agency that we have not been directly connected with. However, we have heard good things about them. Their focus is the unreached, which is where our churches need to be looking. Speaking of that, also take a look at Christar and YWAM. While in South Asia, we met several very solid evangelical folks serving with these agencies.
Operation World - You can find enormous amounts of information about just about any country in the world at this location. This is a great help for churches interested in praying for certain countries.
People Groups - Somewhat similar to Joshua Project, this site lets you look for specific people groups all around the world. You can search by location, religion, language, etc. Click here to begin to look at India's people groups.
People Groups (North America) - Yes, there are unreached people groups in North America. Go here to find them. Some may live in your own village, suburb, or city.
Worldmap.org - I've recently discussed this site, so I won't say much about it here. The best part is the maps - check out India.
Voice of the Martyrs - VOM does an excellent job of reminding us about the millions of persecuted Christians around the world. They have a good bookstore.