I just stumbled upon this thread just now.
I may be a little late but if you're in Amsterdam, check these places out:
(also leidseplein area)
(Amstelveen - a small 'burb SE of A'dam)
These above venues that are not necessarily always known for its indie/alternative scene but it does attract its fair share of lo-fi/indie rock bands. They've attracted acts such as Pavement, the Thermals - but - as well as someone like Willie Nelson. So check their schedule.
Here's more suggestions for hangout places; some of which are great for mingling with the local indie/underground crowd, as they're less well-known; hence, off the beaten path and away from the swarms of tourists. These were recommended by a very good friend of mine who works as a music journalist for deVolkstrant, a local newspaper.
* Winston Intl (Warmoesstraat, just off Dam Square; live indie)
* OCCII (Amstelveenseweg, south side Vondelpark; live punk/alternative)
* Volta (Houtmankade, off Haarlemmerplein; mainly local indie bands)
* Meander (Voetboogstraat, just off Spui; 'danceable' styles)
* The Cave (Prinsengracht, live rock/hardrock)
Hope this helps!