Short answer, it depends what you want.
The guy who though that Prolog was the most powerful was tripping. Logic languages like Prolog are the best for for some unusual domains, but they're actually pretty limiting - a lot of sorts of programs are a lot harder to write in Prolog than they'd be in almost anything else.
I think it might be useful to have the facilities of Prolog lying around in a library, ready to use on the rare occasion that they're a good fit, but I'd never want to write most of a program in Prolog.
My favorite language is one that time forgot, smalltalk. It has a number of features missing from most programming environments:
1. You can save the state of a running program (threads and all), and restore it (sort of like putting a laptop into hibernation).
2. You can debug and rewrite programs while they are running. You can rewrite a routine and restart it, deep inside of a calculation. Programs and data can be edited live. And data can always be saved and reused - you don't have to recreate data each time, or figure out a way to save it and initialize it each time.
3. The entire system, gui and all, has source code available all of the time. It has browsers that make it easy to search through the code and find things.
4. It's just a syntax thing, but all of the parameters are named in a function call - that tends to make code easier to read.
5. The language was designed for humans not computers - it leaves out everything that other languages put in to make programs more efficient for the computer - leaving that stuff out gets rid of a lot of clutter.
6. Since it has no restrictive data typing on variables you're less likely to make a decision early on that limits how you can finish a program.
Unfortunately I'm not sure if I can recommend a great smalltalk system. You can download Squeak, and it's good and has a lot of users, but it's not professional grade. Parts of it have rough edges, and it's not the fastest version of smalltalk.
You could play with the free (for noncommercial use) version of Cincom (runs on everything) - or buy the commercial version if you have $500 to blow.
On Windows you could buy a copy of Dolphin.
Researchers (now employed at Sun) showed that it's possible to write an optimizing compiler for Smalltalk that makes it as fast as other languages, but Sun canned that project and put those people on Java.
...
On the other hand, if you want a language designed to force software to be reliable, (say for medical or military use) you could go to the opposite end of the spectrum and program in Ada. The newest versions of Ada are a good language, and GNU makes a free version (GNAT).
I'm mostly used to C++, but I don't think of it as a good language, just as one I'm used to.
There's a mania for strongly typed functional languages among academia these days. I'm not the hugest fan of those. Some of them have a few nice tricks built into them, but I'm convinced that strongly typed languages force you to "optimize too soon" and make decisions too early in your design process.