In their most basic form, bombs are unguided. For the US military, that means the Mark 80 series bomb, which includes the Mark 81, 82, 83 and 84, with the latter being the largest at 2,000 pounds. These bombs are dropped the old fashioned way, and are what you might see in a carpet-bombing campaign.
On the opposite end of the spectrum, we have the military's Paveway series of laser-guided bombs. They require a secondary source to "paint" a target with an infrared laser. Laser-guided bombs like the Paveway share the GBU designation (guided-bomb unit) with GPS-guided munitions like the Joint Direct Attack Munition, or JDAM. Unguided bombs like the Mark 80 Series and the bunker-busting BLUs can be modified into either laser-guided or JDAMs with a bolt-on kit.
Finally, there are the trusty cluster bombs, which are identified with the CBU designation. The US military's cluster bombs come in both guided and unguided flavors, and can deliver a wide range of smaller submunitions over a targeted area.