Me and my bandmate have a lot of unfinished work. It consists of a riff and/or chord progression (chord progression being the same as the riff), and we're gonna try and finish up some of the songs. Are there any good reads or tips on doing so?
What always worked with my band: jam until you get a song, or at least a solid basis for a song. Try playing another riff or chord progression after the one you already have to change the mood. If it sounds nice, keep it, if it doesnt, jam along. Sometimes riffs are just made to be riffs and nothing else, so dont expect to make a song out of every riff.
A little bit of theory can do wonders as well. If you know which chords will sound good, you can use them as the red thread troughout the song. You always can alter the chords according to your taste by using extensions etc. So it's useful if you know how to harmonize certain scales, the circle of fifths etc.
Yeh dude, the most effective thing you can do is jam the songs out and pick out the bits that sounded best (which are probably also the most memorable).

Whatever you do, don't just say "this is the chord progression" and stick to it- because this stops you from finding anything better!
1. Identify the scale which the riff is created from.

2. Identify the key that the scale is associated with.

3. Use chords from the key to create chords underneath the riff.

4. Extend chord structure to create full song.
And no, Guitar Hero will not help. Even on expert. Really.
Or to play the devil's advocate..... from a technical copyright perspective, a song consists of melody and lyrics. Chords and riffs don't count. Chords and riffs are the clothing your song walks around in, but you still don't have the person to wear them and do the actual walking around. Just as easily as a person can change their clothes, you can take an existing melody and lyrics and change or remove or add riffs, and you can often times even substitute chords so that the chord progression changes. It's still the same person, just wearing different clothes, and everyone can still readily identify that person.

First example that comes to mind.... Tori Amos' cover of Smells Like Teen Spirit.

Comparatively, you can take a famous outfit - say the one that Michael Jackson wore in the Thriller video - and get someone else to wear that outfit..... say, Adam Sandler. You're not fooling anyone. Nobody will actually think that is the same person, just because he's wearing the same clothes.

Example - Oasis' Wonderwall and Green Day's Boulevard of Broken Dreams. Same chord progression, but undisputably different songs.

Could I get some more talent in the monitors, please?

I know it sounds crazy, but try to learn to inhale your voice. www.thebelcantotechnique.com

Chris is the king of relating music things to other objects in real life.