I've been a happy user of the Ethnologue database for years. It lists all languages of the world in a simple database form. Just yesterday I did a search for Malagasy ethnologue to learn that Malagasy is a language of Madagascar. It's a lot of fun to browse, skipping from country to language to country as you follow immigration patterns.
The New York Times today has an interesting article about Ethnologue, on the occasion of the publication of the new version of the database. I had no idea the database was developed by Christian missionaries! In retrospect that makes perfect sense, just like LDS maintaining the best geneaology data. Sometimes religious fervour has practical benefits. I also didn't know Ethnologue is the source for the three letter language codes we use in internationalized software, soon to be ISO 639-3.
Don't miss the NYT's visualization of language distribution. I love the NYT graphics; this one is by David Constantine.