I would try to find an inexpensive tutor who's a native speaker. Even if you can't afford a lesson every week, the tutor could make sure you are on the right track with your pronunciation.
The problem is that English learners have trouble telling the difference between certain vowel sounds in English. Because of this, they can't tell if they are making the sound correctly. After they hear the sound correctly for awhile, and after the teacher has worked with them on the correct sound, they can eventually (usually) start making the sound correctly. A few of my students have trouble hearing the sound of the short e in the word bet, for example. Sometimes they say something that is between the word bet and bat in English.
I don't deny that practicing with a proffesionally trained native speaker is the best option. I agree with you, Daniel. But I wonder, what would you suggest to a person who cannot afford professional lessons with native speakers (like me for example)? It takes more than one lesson to make any progress, especially when it comes to pronunciation.
I agree that practicing pronunciation with non-native teachers may be risky, and this is why I've suggested to listen to the BBC podcast and use some books. I'd also suggest to learn the IPA (international phonetic alphabet) in order to be able to check the pronunciation in dictionaries, etc. This is how I learn pronunciation and I don't consider it ridiculous, I believe it helps to start this long process.
You really need to work with a native speaker. Otherwise, you will think that you are making the sounds of your target language correctly, but in reality you will not be. Your ear is simply not trained well enough to tell the difference.
There is a huge difference among various tutors and teachers. Some teachers will not correct your pronunciation unless the teacher can not understand the word you are trying to say. Some of these teachers think that your pronunciation will eventually improve on its own because you are continually being exposed to correct pronunciation. (I think this is ridiculous and doesn't happen in the real world,) Other teachers realize that the student is not going to suddenly pronounce words correctly, but they don't care, and they actually "like" the sounds of the mispronounced English. It sounds "exotic" to them. (Again, this is only if they can understand what word the student is trying to say.)
Other teachers work on pronunciation and try to get the student to sound as native as possible. If you want a teacher like this, you need to specifically tell prospective teachers this. Even then, they might not correct you.
I don't think a language partner can help you. Most are not trained to deal with pronunciation issues. Try to find a tutor, and tell them that you want to correct your pronunciation. Even then, they may not be able to deal with it. The right teacher could help you, but taking lessons every week is expensive.