In responce to Azreal's first paragraph, and the thread as a whole. What makes a certain solo stand out and become memorable is a good melody. The most paladable thing to the listeners ear, so if you can outline a melodic tune with your solo it will have a better chance of being liked by the listener. If not you can always smile and shrug knowing that they will drive themselves crazy cause they can't stop humming it. :D

As for good places to start. Think of the chord or key your soloing over. i.e. C major. Now think of what notes make up the C major triad, C, E, G. Any 3 of these notes is a good starting point. Try C using the C minor pentatonic over a C major chord. Contrasting but interesting. Think of each scale as a different color of harmony that you can apply to an individual chord or entire key.