In short, the problem seem to be that my client believes it has broadcasted a transaction to the network while the network doesn't seem to have recieved it. So how do I "re-broadcast" this to the network?
It's a 33 BTC transaction to 13L7sQqXELU8xuwBjMqb8uDUqNojtpiHY btw if anybody wants to look it up.
Edit: I should really search first. Anyway, I found another thread that says the client will try to resend the transaction every couple of days though. This is kind of bad though since the transaction is going to Mt Gox and the adress is only usable for 24h.
I'll try to obsessively restart my client as mentioned in the other thread and hope it works, but if it doesn't I think this really needs to be solved before the Mt Gox adress expires.
Edit2: Yes, it does seem like obsessive restarts solves the problem :-)