We've just had the Party of European Socialist's Congress at the end of September, but the congresses of the other Europarties are still coming up. The European People's Party will hold their Congress this week in Bucharest on the 17th and 18th, which you can follow here.
The other Europarty Congress dates are:
European Liberal Democrats: 8th-10th November, Dublin.
European Greens: 9th-11th November, Athens.
I wasn't able to find Congresses for any of the other political parties, but I did find that the European Alliance for Freedom (part of the anti-EU Europe of Freedom and Democracy Group in the European Parliament) held a Congress on the 24th-27th June in Malta. You can find it here, but there doesn't seem to be much in terms of policy or tactics that came out of it.
So though there are 12 recognised Europarties as of 2012, there only seems to be Congresses for a minority of them (though they are the big mainstream Europarties). Their activity needs to ramp up next year in the run up to the 2014 election if they're to prove their worth.