Suggestions from me, since I was in a similar place a short while ago:
Check out this site:
http://www.zentao.com/guitar/theory/
Very nice, easy explanations with diagrams.
Chord suggestions from me:
Understand that most basic chords are built by stacking thirds on a root note.
Learn how to build triads (3 note chords) first. Triads come in 4 forms:
Major
Minor
Diminished
Augmented
All of the above are simply variations of the "stacking thirds" idea. Remember that thirds come in two flavours: major thirds (4 semi-tones) and minor thirds (3 semi-tones). To build the above chords:
Major - Root + Major Third + Minor Third
Minor - Root + Minor Third + Major Third
Diminished - Root + Minor Third + Minor Third
Augmented - Root + Major Third + Major Third
Simple as that! Take a root note from a scale, and write down the notes for each triad for that root. Then check against a reference to see if you're getting it right.
Once you're happy with that idea, take a look at 4 note chords. Again, start by stacking another third on the triad you've built, and suddenly you're playing in the realm of 7th (and other chords).
Then, take a look at learning the chord scale (or what some people call Scale Tone Chords). This is the basis of chord progression theory, the whole: I, ii, iii, IV, V, vi, vii, VIII idea (well, using the major scale here).
You can learn to play the progressions using triads as well as 4-note chords. Start with common, easy-to-learn ones like C and G.
The guitar isn't really what I would consider a great "inversions" instrument, compared to, say, the piano. I would hang on with inversions until you've looked at the above.
In my opinion, once you've learned the thinking behind building chords and progressions, it becomes much easier to "memorise" those shapes. It also allows you to work out fingerings on the fly, rather than having to consult a chord dictionary every time someone calls out a chord you haven't used before. I suddenly found myself digging into chords and progressions I'd never considered before!
Honestly, it also doesn't take that long for someone who is already quite familiar with the instrument. You can absorb these basics in a few readings. Of course, the trick is to sit with the instrument and really learn how to PLAY them, get the shapes into muscle-memory. But this particular bit of theory has de-mystified a ton of stuff for me.
Added bonus: once you understand the building of chords and progressions, suddenly using modes becomes SO much more intuitive! This will help your lead playing immensely too.
Other really handy sites:
http://en.wikipedia.org/wiki/Triad_(music)
http://en.wikipedia.org/wiki/Interval_(music)
