What are the different platforms you launch your project on?
…and general forums where applicable.
Same & many links from Places To Post Your Startup & Which MarketPlace
The more the merrier. Although sometimes negative backlinks can ruin the SEO, you can't know for sure where your customers hang on. You just need that one customer who has a big following in the market that you are targeting.
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BetaList and depending on the product, specific forums / communities.
There is this little community called WIP - they provide awesome feedback.