For Heimer, champions with long range abilities are quite good at clearing out his turrets. I've had really good lopsided matchups as Sivir, Cass, and Caitlyn against him. Clear his turrets, and harass when able. Without his turrets, it's really easy to push against him and/or outright kill him. Melees generally have the most trouble against him.
For Yorick, well, he's considered the god of bot lane by many. I've had the most success against him as ranged ADs, especially Sivir (as Yaladilae said). Once you get your lifesteal engine online, you can actually heal off of his ghouls. Just don't die early.
For Singed, I've always found he crumbles hard to ranged harass, especially if you have some kind of hard CC to add in there. Ryze works really nicely against him. Chunk him with harass whenever he gets near the creeps, and if he tries to go in against you, just snare him and continue kiting. I think Singed is actually a rather poor choice for bot lane overall.
For Maokai, turbo pushing seems to work alright. He can clear waves alright with his Saplings, but many champions can push faster. If your opposing Maokai levels Sapling Toss first, you can get in and be very aggressive against him early game. Wait for him to burn Sapling Toss on minions and dive in there. He'll be without his major damage skill for a pretty long window. And like Yaladilae said (again), don't fight him in his ult if it can be helped. Most of the time, you can just calmly walk out of it.