I'm a indie/hobbyist game developer.  How do I check that I'm not infringing any copyrights or trademarks when I release my game?

I'm not making megabucks so it's not financially feasible to get professional legal help for each game.  

I asked recently [if I can reuse the name of an old arcade game][1] (Crazy Balloon), but this got me thinking about future games where I might not even be aware of something similar that existed before.

So, are there any tools or resources that you can recommend to check myself (due diligence I think it's called).


  [1]: http://gamedev.stackexchange.com/questions/14908/can-i-reuse-the-name-of-an-old-arcade-game