I've organized some small/medium (6 000 - 10 000 people/event) events in Tampere, the latest one of them was less than two weeks ago so my info is somewhat recent. My speciality is project management (in event planning) and I've got quite idea how to do logistics and security things for events. I'm not much use in programming, but that's not going to be a problem, as we all can se from the great suggestions we've got so far! :)
The main point you must know before choosing the location is: how many people are you aiming at? I'm guessing in thousands but is it closer to 2 000, 5 000 or 10 000 or more? The location for 2 000 people is way easier to find than a location for more than 10 000 people. Here are some examples (and price ranges, too):
2 000 people: The Tampere-talo big hall has space for nearly 2000 people but it's damn expensive. Tampere-talo was a tad too small for nearly 10 000 people even though we got the whole building... The rent was _high_ but then again the quality of the service was good.
5 000 people: The Siperia area fits 5 000 people nicely. There is no place in Tampere which would fit 5 000 people at once (one room, that is), apart from Pirkkahalli, which might not be the best idea. Siperia area has the movie theatre, restaurants and room for exhibitions and program items, if you want those. The problem is part of the buildings belong to the city and the people who work there won't stay in longer even though one would be willing to pay more rent for them to do so. We've had this problem (and we had it less than two weeks ago) and that's the reason we're thinking of organizing the event somewhere else next year (but nothing has been decided yet). The prices can be and aren't _that_ expensive but not cheap either.
Pakkahuone, Klubi, Telakka and all the things around it are good but I haven't organized any events there yet so I don't know about the prices or how the thing actually works. But it's good for evening gala type of a thing (especially if there's both Klubi and Pakkahuone in use). Telakka is a cheap place to rent and it's possible to have an art exhibit on the second floor there but the place isn't really "Iron Skyish" to me :)
For 10 000 or more people I think Tampere-talo is on the edge and Pirkkahalli is the place where people would actually fit. Both most likely extremely expensive (at least Tampere-talo is) and Pirkkahalli is _really_ far away from the centre and everything else (hotels, etc.)
For an even any size the security things are quite important and the police bureaucracy can ge a pain in the ass. In Tampere it's usually best if you have people who have organized big events before filling the applications because police likes the big events in Tampere as the security things have always been handled well.
If you need any opinions, help or anything else, you know where to contact me. I'm willing to help you guys! Just let me know if you need my help! :)