Bissell's Quicksteamer works pretty good.

We have light colored carpet and seven indoor cats, so our carpet needs to be steam cleaned from time to time.  Rather than pay someone to come into my home, we opted to by Bissell's Quicksteamer.  We paid about $80 for the steamer at Wal-mart.
The Quicksteamer is very easy to use.  First you will need to fill the water compartment with hot water, and add your detergent.  Make sure you do not fill the water past the fill line or else you could end up with a mess on your carpet.   The water compartment comes off the steamer very easily and slips right back into place.  Then your ready to steam away.
Steam clean your carpet with the steamer like you use a vaccuum.  You will need to press the trigger for water to come out, and then run the cleaner over it for a few times to get all the water sucked up.  It does a good job at getting most of the water up, my carptets are just damp after I have cleaned mine.
My carpet looks fresh and clean after I have steamcleaned them.  You can really tell a big difference after I have done them.  And you can see the dirty water as you pour it out so you know it has done its job well.
I have had this steam cleaner for about 6 years now and it is starting to die on me.  But I have gotten my use out of it and would recommend getting one of these to anyone, especially if you have kids or pets.
Some tips that may be helpful to use with this is to make sure that if you run out of water doing your carpets, as you fill up the water tank, make sure you dump the dirty water.  I made the mistake once of not dumping it and the tank got too full and dirty water started squirting out all over the place.  And dump the dirty water every time you are done with the machine so it does not get smelly or musty.  You should also clean out the machine with clean water and clean out the little trap inside the machine.