Below are the options I was looking at when I was trying to figure out how to heat my tank. I ended up going with (6) 300W Eheim Jagers (for a total of 1,800W) with a Ranco Temperature Controller:
http://www.jehmco.com/html/temperature_controller.html.
The reasons I went with the Jagers and the Temperature Controller:
1. Cost: By far the cheapest option at only $240 for the heaters and controller. All the other options would have cost me quite a bit more to get the equivalent wattage.
2. Safety:
If one of my heaters fails, that only knocks 300W off of my total wattage. If one of the larger units fails, I would need a complete replacement (way more expensive to have backups). Also, the 1,000W heater sticks get VERY hot, since they have a smaller surface area. All 1,000W goes through one small titanium heater stick, versus the Eheim's equivalent wattage being spread out over several 300 Watt heater sticks. The 1,000W heaters are more likely to fail for this reason.
3. Reliability- Jagers have a history of being great heaters and the Ranco Controllers are used for all sorts of applications and have proven to be very reliable.
4. Ease of use: I did not have to completely rearrange my plumbing, which I would have had to do if I had gone with an inline heater.