try this site; Just follow the steps to find which ending the adjective needs. It works and you get used to it quickly. There's lots more. I wish there were some way to go back and find the name of the "classmate" who first posted this to say DANKE.
Thank, that is helpful, but even with this chart it is very, very hard to remember all these rules, and to recall them quickly when speaking/writing. I guess this is one of the hardest topics in German grammar.
Now it's my turn to say thanks. My laptop crashed and I lost lots of info (most was backed up but not this lovely site) can't tell you how happy I am to get it back. Here's another site I like because I can listen while doing other things: http://www.youtube.com/user/ElonGermanStudies
The audio seems to be saying "Wo ist DER schwarze Auto." This needs correction.