What I refer to with 'underground clubs' are not commercial or not Ibiza-style housy clubs. I mean more electronic music like minimal house, minimal techno, electro, techno, etc. with alternative people. Trance doesn't have much acceptation here, so there's not a regular club playing trance here.
As you're coming in August you likely won't see the city at top gear, as this is the month when most people fly away (July is much more interesting and has lots of things and festivals in the city), but surely you will find the places still amusing.
Apart from Buddha del Sol, which I have explained above, you can try on the same way (South along the coast) Apache Valencia or Puzzle. The first one is nearer to Valencia, at Pinedo, only 5 minutes by taxi, beside the sea, but they have some different rooms where they play latin music and classic dance besides the house room. You might find in it a good place though, and it has terrace too. Puzzle is pretty far, at 2kms past El Perelló, takes 25-30 minutes driving through the natural park Albufera. It's more wicked and it has two rooms (tech-house and funky/tribal house). They use to bring the most famous DJ's in the world regarding house.
Both venues are trendy and beautiful places too.
Just in the city, you can try two terraces for the first drinks or to chill out a little (they close early, at about 3-3'30 am): Ghandara, at las Arenas beach, and Lupita Beach at the gorgeous terrace Flamingo, located at Malvarrosa beach.
Housy after-hours: Friend's Club, and Sundays @ Puzzle. Sundays is upstairs the club Puzzle (not the whole club) and is more housy but a bit small. Friend's opens Sundays at 17h to 7am. It's a big covered terrace with daylight by day. They play from house to tech-house and some techno depending on hours. Lupita Beach also opens in the morning on Saturday and Sunday, but this time it's more aimed to alternative people.
On Thursday nights, the housy people use to go to the Summer Experience parties at Giorgio & Enrico, or to the Summer Addicted Parties at Café Cantante. The first one is one of the trendiest places in Valencia, and it's big, located on the northern outskirts of Valencia. The second one is quite a small club but beautiful too just inside the city.
From thursdays to Saturdays, another very trendy and classy venue (too posh for my liking like Giorgio) is La Indiana, near the center of town. I think they have closed in August though.
There's another important club called Guru but I think they closed their season in July and will reopen in September.
For the first drinks, the best place in the city is the neighborhood El Carmen, in the old center of town. There's an assorted and bustling life there.
Websites:
Apache Valencia (just Saturday night):
http://www.apachedisco.com/
Puzzle (just Saturday night):
http://www.discotecapuzzle.com
Gandhara (everyday):
http://www.gandharaterraza.com/
Friend's Club (Sunday afternoon and evening):
http://www.friendsvalencia.com/
Lupita Beach:
http://www.zonadeclubs.com/clubs/terrazas/lupita/pub_lupita.htm
Giorgio & Enrico:
http://www.giorgioenrico.com
Guru (not sure):
http://www.gurudisco.com
La Indiana:
http://www.laindiana.com
I didn't find any website for Budhha del Sol or Cafe Cantante at the moment.
for general information:
http://www.turisvalencia.com
http://www.valencia.es
http://www.cac.es (City of Arts and Sciences)
http://www.thisisvalencia.com/ (just in English for English speakers)
I hope this helps you spend a nice and fun stay after all this job I made for you, hehe!

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