It all depends what you're wanting to get out of the rave. The easy option is to just go to something like GoodGreef or something. That sort of thing's advertised with flyers and posters all over the place. I find more rewarding and entertaining are the 'less advertised' raves. They tend to have a much nicer atmosphere, but you have to know somebody close to the organiser. There's quite a few happen over the summer months up here in Cumbria, but it's really just a matter of knowing the right people. If you've heard of any locally, just asking some folk's your best bet.
It's well worth going to a rave, even if it's just an organised one at a proper club - it's a hell of an experience. Certainly something you should have on your list of things to do before you die.
Hope I've been of help, and good luck in your mission!
I have to agree with xander. a smaller less mainstream rave is a much better option. even things like burning man can be a totally different experience than you think(so I've been told, haven't made it myself yet) in part because of the size. also keep in mind the easier it is to get to a rave the less responsible the people who show up. I suggest a campout type event as there are no worries about driving at the end of the night and you have more time to have fun, spin fire etc. I can't suggest anything local as I'm in the states but keep your eyes open and you'll find what your looking for.
For my two cents, I much prefer "Burns" to "Raves"...
Burningman.com has links that you can follow (start with the "regional contact" link under the "stay connected" tab) to connect with your local Burner community. It has become rather well established in Europe from what I understand. Burners tend to be more responsible (radical self-reliance, civic responsibility, communal effort, leave no trace) more creative (radical self-expression, decommodification, gifting economy) and more akin to fire (duh) than your average raver who is falling into or crawling out of a K-hole. Not that I haven't had good experiences at raves, but at best they are a mixed bag and they can actually be quite scary if the wrong people show up (Cops, shady drug dealers, thugs who rob shady drug dealers, etc.)...
Also, there is an established network that you can use to connect with Burners in your area since we also practice radical inclusion. So, check out the website, do some background reading (at the very least, you should familiarize yourself with the 10 principles, some of which I have mentioned here) and hook up with some of your regional networks. Once you have made those connections, you will start to hear about events happening in your area.
And hell, Burners have been known to rave, but once you have been to a Burn they will seem rather one-dimensional by comparison, trust me. Basically, a rave is a night-long dance party, and most regional burns have that and much, much more. But still, connecting with local Burners might help you find local raves as well.
Nowhere is the European Regional Burn held annually in the Spanish desert. I plan to make it out there some day, so maybe we will run into each other;)