You have to make sure to buy a heavy duty, preferrably professional grade pan. Thick base. Most important. I have owned my pans for about five years, and nary a warp. Completely flat. I also have a glass top stove. Note to the wise, do not use a dishwasher to clean good cookware. Always clean pans, pots, knives, etc. by hand.
Any good restaurant supply house will have good quality non stick pans. Also, I' m not sure where you live, but many large department stores (JC Penny in the States, the Bay here in Canada) have good quality wares. Be aware, they do not come cheap, but they will not have to soon be replaced.
Most reputable sources say that curved surfaces such as woks don't work as well on induction stoves. They even make special tools and cooktops for inductively heating woks. This phenomenum could be because of the angled surface or the extra distance from the cooktop, but it's probably both. It's not that these surfaces are immune to induction heating, just that they aren't efficient.
Angled surfaces won't respond as well to induction stoves since the maximum amount of energy is generated in a surface when it's flat with respect to the stove. (Magnetic induction is proportional to the cosine of the angle between loops, for those of you who want to know the physics).
Distance is probably the biggest factor. Induction works at a small distance from the stove (there are numerous examples on the web of induction heaters working through newspapers or a magazine.) However, the design of these cooktops makes it so the magnetic field that drives the heating dies off over a very short distance (For example, the Swiss Federal Office of Public Health determined when studying their effect on pacemakers that the field is negligible after 10 cm or 4 in).
As far as what materials work, usually cookware that's induction cooktop compatible has a curly icon on the box to indicate this. Common compatible materials include magnetic stainless steels (not austenitic steels), iron, and carbon steel. The article on induction cooking on Wikipedia has a great explanation on what cookware works for induction cooking and why.
There common rule of thumb is that if a magnet sticks to the bottom of a pot or pan, it's compatible with an induction stove. Surface resistance is a more scientific measure, but to get the complete picture of why certain things do or don't work would require a college course in material electromagnetics. For a more detailed analysis, see the wikipedia page I linked. For most cookware these are only minor concerns compared to the magnet test, until you accidentally leave aluminum foil on an induction stove and it starts to melt.
It should be noted that cookware needs some inductive metal in it, but not all of it needs to be an inductive metal. Some cookware designed for an inductive stove has an iron bottom with aluminum sides because aluminum conducts the heat better for more even cooking. Clad cookware with a mixture of the right metals works too.
Best Answer
What I would do is invest in a $30 - $50 single induction hob that can be put on your counter, and see if the problem persists there. At the worst case, you just have an extra hob for stocks or something, but it could very well be that you'll have some success there, which gives you a hob that you could use for searing and such. It helps you to eliminate the range itself as the culprit.
The other thing you could do (again, any action here is going to cost money) is invest in some 3 or even 5 ply cookware from a vendor like All Clad. They have steel / copper / steel / aluminum / steel 'sandwich' pans that are tested to conduct heat perfectly evenly.
Given what you've tried, I tend to think the range itself is the culprit. Some induction ranges (especially earlier ones) just didn't perform very well for cooks that ventured beyond basic boiling and frying. This is why getting an extra hob might be the best course you could take.
If it is the range itself then high-tech / high-performance layered cookware is going to probably help a little, but it's not going to fix the fact that the rings aren't functional comparable to the dispersion of a flame (which modern hobs can mostly claim, even the cheaper ones).
While cast iron isn't guaranteed to be an even conductor and can have its issues, those issues shouldn't be nearly as bad as what you're seeing, which strongly points at the range itself as the likely culprit.
Good luck, unfortunately this is one of those problems that requires a little spending to figure out.