Unless they happen to have added a new one in the most recent content patches that I missed(1.2.3), I only know of two. One is the Nether Portal, which can be made from Obsidian and lighting the inside of it on fire with flint and steel. The other is the portal to the End, which you will have to find and activate inside of a stronghold that you can find generated in your world (you will want to create Eyes of Ender to help locate/activate this portal, which can be made with one Ender Pearl and one Blaze Powder).
The "Aether" mod did include a third kind of portal, made out of glowstone and activated with a bucket of water, but that portal is not available in vanilla Minecraft, and there is currently no version of the Aether mod for any version of Minecraft past 1.0.0 (However, I have heard they are working on "Aether 2", a sequel to the mod, for a future Minecraft release).
· 8 years ago