mWMP's volume is also dependant on the system volume. I have a phone profile that starts at 5p and lasts an hour, for louder ringtones. If I'm listening to music when it inables/disables, it often gives me pause...
Success100, MP3Gain isn't as cumbersome as you might think, as it supports playlists and drag/drop. It'll batch analyze and adjust groups of files (though some hand-tweaking on a couple files might be necessary.) If it's only playback on a mobile device that's the issue, then it's not necessary to go through one's entire library. And, since it's only changing a ~loudness playback flag~ on the MP3, and not re-encoding the file, it's fast, actions can be undone, and it dosen't introduce degradation of the audio.
Sarah, you might try Audacity for editing your wavs & MP3's as ringtones. It's a PC based waveform editor. (Freeware) It has quite a few filters, maximize sound w/o clipping, taper lead and ending, downsample HQ MP3 clips for ringtones.. (There's no point keeping that 192kbp quality on a 30 sec ringtone.) Very handy little app.