Youlean Freq-Balancer is simple tool that will help you with mastering by balancing frequency response of your songs. Try it on your master track! There is a demo, and the full plugin is donationware. I bought it straight away, and it sounds great as it easily equals out the frequencies of your track in a way that you would spend hours working on EQ.
Freq-Balancer analyzes the frequency content of an audio signal and automatically applies an equalizer that evens out the frequency balance towards a curve found on many commercial tracks. When Freq-Balancer analyses audio, it measures the audios frequency content over a period of time. It splits the incoming audio signal into 7 frequency bands. Then it measures and compares the audio levels within each band. Finally it applies EQ to compensate for any uneven frequency balance.