Dante is very clever! All of his punishments correspond directly to the sin. For example, Lucifer, the greater sinner of all, is in the lowest level of hell, where he sits stuck in a frozen lake. The lake is frozen because his large wings constantly blow cold air, keeping it perpetually cold. Dante gives Lucifer three heads, which is a twist of the Christian Divine Trinity (God the Father, God the Son, and the Holy Spirit), each of which eat three of the most well-known traitors from history-- Brutus and Cassius (betrayed Caesar), and Judus the Iscariot (betrayed Christ). With this depiction, Dante is highlighting that Lucifer himself was a traitor, which is apparently the greatest sin (since the other three are in the lowest level of hell as well), and that his punishment is something that he still causes.  

Oh, there are many!!

All of the nine circles of hell are symbolic of divine retribution for earthly sins.  (Picture a funnel, with the widest circle at the top, and the smallest at the bottom.)

Here is a quick run-down of levels, some of the inhabitants, their crimes, and their symbolic punishment:

Upper Hell, The Incontinent ("Incontinent" here means "wanting is self-restraint") Residing here, among others, are the Lustful, the Gluttonous.  Those who were lustful on earth are condemned to being tossed around relentlessly by a storm.  The Gluttonous are punished by a pounding, ceaseless rain. 

Lower Hell is reserved for the Violent and the Fraudulous.  Here, in the sixth circle, reside the Heretics (those who disobey Church law).  These souls reside in endless tombs of fire.  Among the violent are those who have committed suicide.  They have been trasformed into trees, and vicious Harpies, (ravenous bird/woman monsters) who eat their leaves each time one sprouts.