Singed is my default hero and I love him. I'd like to make a few suggestions however.
1. He is very rarely (never) played. I know people tend to play the Flavour of the month hero, but I think singed could use some love.
2. The range on throw could be increased very slightly to catch someone behind a mob. I find it horribly difficult to slalom between creeps just to try to grab someone (cf comment on poison trail).
3. Poison trail's range is too weak. I sometimes find myself hitting a mob and not applying poison to it. And, again, it is quite difficult (not to mention dangerous) to have to slalom between creeps, although it's probably part of the character. To be more specific, when creep waves collide, there are two groups. The melee one and the ranged one. I should be able to go hit the middle creep in the range group and apply poison to all three of them, which is rareley the case. And I'm not mentioning neutral creeps that require you to move around them to reapply the poison.
4. Super sticky applying poison would be great and would improve singed, but I'd understand that its sole purpose is to slow.
Other than that, he is great. Design-wise, and all. Great job.