If you have some money to kill and like the more "design" oriented tanks, you might want to consider the Fluval Spec V (5 gallons). Retail is 99$, though I've seen that it goes on sale occasionally for around 70$. It's in the same general shape as the bookshelf aquarium, but with a nicer look to it. I have the smaller 2 gallon version and it works perfectly for my betta. The filter is nearly silent and there's enough room to fit an adjustable heater along with the filter itself in the hidden back compartment.