How much music theory do you know? Music theory, the more complex stuff in particular, can assist you greatly if you use it correctly.
And have you tried working the opposite way? Instead of making a chord progression first and then adding a melody on top of it, try making a melody and then throwing chords under it. If a melody's good, chances are it has a great-sounding chord progression too.
For instance I can't work by making chord progressions first. In the rare occasion that I come up with a great chord progression on its own, the melody that comes out on top of it is terrible because it sounds exactly like I'm trying to "force" it into the chords, if you get what I mean. Then again, I have friends who work the other way round and their music is amazing, so it's all in which approach you prefer.