What are some good places to get sound effects and what to avoid?

• http://freesound.org/
• http://opengameart.org/art-search-advanced?keys=&field_art_type_tid%5B%5D=13&sort_by=count&sort_order=DESC
• http://www.flashkit.com/soundfx/

Pay attention to the license requirements on each item.

You may want to grab Audacity (http://www.audacityteam.org/) as well for tweaking things and possibly for recording your own effects. With a little patience and creativity you can make most simple effects yourself.

You can also make your own on http://sfbgames.com/chiptone/

You can even save ("save setup") to work with it later.

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http://soundimage.org/

This guy has some good sound fx but doesn't have a lot of them since he mainly composes music.

It depends greatly on what kind of sounds you are looking for. Synthesizers are good for some sounds. Some sounds can be found on the internet as some have pointed out. You may have to record your own. A digital recorder is probably a good place to start for that. I'm sure your setup can become as expensive and as involved as you want it to be. In addition, you will probably want at least some simple audio editing software for cutting out parts of the track you don't want if nothing else. And recording is a skill like most everything else. It takes time and practice to get good at it. And more equipment.