LOUISE,
Well one thing to keep in mind is that there's still not an EXACT science as to what will truly be stronger, as everyone reacts differently to every pill.
But I think probably a safe, general rule of thumb would be that things like Ultracet/Ultram and Darvocet (propoxyphene is the generic) are the weakest prescription relievers you can get, while still being technically Schedule III narcotics. The next step up would be hydrocodone, which comes in many brand names like Vicodin, Lortab, Lorcet, Norco, etc. And it all comes in varying strengths. The weakest hydrocodone pill you can get is 5/325 (5mg of hydro & 325 of tylenol - although now that I think about it, I'm not 100% sure hydro comes in that exact strength - otherwise the weakest combo would be 5/500. There are several differnt combo amts, 10/325, 7.5/750, 10/500, 10/650... you get the idea
The next level up would be oxycodone, which also comes in varying brand names (Percocet, Percodan, OxyIR, Roxicodone, etc). Oxy is a Sched. II drug (stuff that's Sched I is only like heroin, cocaine, etc). And just like with the hydro, oxycodone comes in all the same varying strength combos.
Keep in mind all the examples I just gave you are all SHORT ACTING MEDS. Currently, that I know of, hydrocodone comes in no LONG ACTING FORM. When you're RX'd a LA med, there's no tylenol, because it's with the understanding that you're going to be taking it for awhile. (believe it or not, most people in America who are given Vicodin, it's only for a week or so, so that amount of tylenol is negliable to them). Oxycodone DOES come in a LA form, that's what OxyContin is. You may hear a lot of people on here talking about taking OxyContin as their base med, as they use some form of Percocet or OxyIR as their "break through" med. These people are taking the same exact drug both times, they're just taking it in two different forms. (The Contin sustains an even level of the drug in your system during the day - well, supposedly

and the regular oxycodone product gives them an immediate boost for acute pain a few times a day.) There are other LA meds that don't contain oxycodone, but it's up for debate which ones are stronger than others exactly. Like I said, it just depends what works for you. MSContin is a LA morphine product. I'm sorry, I feel like there are other LA pills that I'm forgetting right now. There ARE two other meds I can tell you about, but they're kind of different. For one there's Methadone, which is also what I'm on. Technically, this isn't a LA med in the same formulation as the OxyContin or MSContin is. It doesn't release an amount of its power after you take it, then slowly do that again at the 8 or so hour mark, like those other two do. Especially in my experience, it seems to work actually more like a short acting med, it just happens to work on you for a long time. Does that make sense?
The other one I was thinking about is the Duragesic, or Fentynal Patch. I've never used it, but is one of, if not the most potent opiate reliever RX'd. It's simply a patch you put on (like the 'quit smoking' patch, if you're familiar), and over the course of 48-72 hours it delivers you a steady constant dose of fentynal. You have to be in some serious pain for you doc to give you these. There are of course varying strengths.
Okay like I said, I decided to reply here because I wanted to, and thought, that I could help you, but now that I'm writing I feel like I'm forgetting others. But hopefully at least that'll give you a general idea of the sort of 'ladder' of painkillers there are. Good luck