I wouldn't say that one particular niche is always hot. Right now from what I'm seeing is anything to do with Finance, refinance, loans (as you mentioned) BUT saying that, anyone can reg 20 domains with those words in them but they have to be understood by the "internet general public" as typed in traffic. So if you had (again, I apologize if I actually mention anyones domain out of context) RefinancedLoans.com and you had the choice between selling that or BlueGrassFinance.com, which one do you think would have a better chance? Common sense right? Use common sense terms when buying or fresh regging a domain.
If you want to know whats the hot topic of the year, watch the news, read the newspapers, see whats being said everyday, every broadcast and make your judgements from there. Again, it's up to you which way you swing with your domains but what I'm saying is just my opinion, always remember that
