OK, get out the wine, light some aroma therapy candles, and practice your very best FM radio DJ voice, because we are going to cover some of the cooler, laid-back chords.
Specifically, we will cover the Suspended 2, Suspended 4, 6th, and the Major 7th (not to be confused with the Dominant 7th--the one you are probably used to).
Suspended (sus) ChordsHere are the patterns:
Sus2: 1, 2, 5
Sus4: 1, 4, 5
Pretty easy to remember in context of the major chord 1, 3, 5. Just replace the middle 3 note with a 2 note or 4 note.
Sus4Let's start with the sus4 because it's the one you probably hear more often. Let's say you're playing a ballad in G and there is a measure or two between verses or between the chorus and verse where you just hang out on the G. Instead of just rolling on the G chord with open strings, try starting with the 1st, 2nd, and 3rd strings open, but then play the 2nd string on the first fret for a beat or two (continue playing the 1st and 3rd strings open), then come off. That is a Gsus4 you're throwing in there when you fret the second string on the first fret. Experiment with how long to hold it before coming off. Like with most of the color chords, less is probably better. To me it has the effect of watching a paper airplane gliding to a landing but then at the last second it wafts up one last time for just a second before it touches down.
You can play a sus4 on any of the bar chords by starting on the straight bar chord, then slide up one fret to the 4 note on the middle string (mute the other two) and then slide back down to the 3 note in the straight bar position to come out of the sus4. Once again, decide how long to hold the 4 note based on the effect you want.
Sus2To me the sus2 has a very similar effect as the sus4, and I use it much the same was as a sus4. A Gsus2 is easily played by playing the 3rd string open then hammering the 3rd string on the 2nd fret then playing the one string. Here is a roll pattern that Jerry Douglas uses in the key of C. It is built on the Csus2 chord (because of the open 1st string which is a D), which provides its distinctive sound. 
6thThe Major 6th is a jazzy little chord with the pattern: 1, 3, 5, 6
An easy way to play a G6 is just play the 3rd, 2nd, and 1st strings open and then hammer on the 2nd fret of the 1st string. That gives you a G, B, D, E.
If you've ever heard Panhandle Rag and wondered where it gets its jazzy sound, it uses D6 a lot by barring on the 7th fret but leaving the 2nd string (B) open. (D, F#, A, B)
Here is another Jerry Douglas roll exercise that is built around a D6 chord. The open 2nd string is a B. 
Note: You can also play a Minor 6 with the pattern 1, b3, 5, 6.
Money NotesThe 6th chord is the first chord we've talked about that has more than three notes, and so this is a good opportunity to talk about an important principle of playing chords with a Dobro, Namely:
You don't have to play every note in the chord!
Sometimes the combination of key, chord, and melody just make it darn near impossible to get every note in. In these cases, you want to let the Dobro stress the "money note," that is, the one that really establishes the chord you are playing. To find the money note, just ask yourself "How is this chord different from just a plain old 1-3-5 major chord? In the chords we have studied so far the money notes are the following:
- Flatted 3rd in a minor
- 2 note in a sus2
- 4 note in a sus4
- 6 note in a 6th
Playing a 1, 3, 6 or a 1, 5, 6 gets you even closer.
What about all those other other notes you're not playing? Hey, you're not the only one in the band or in the jam! Whoever is playing rhythm will pick them up, or if they are in the melody line, the singer or whoever is playing the solo break will pick them up .
Major 7thThis isn't the 7th you're used to playing--that one is a dominant 7th, and we will talk about that one in the lesson on transition chords.
This one is the grand daddy of cool chords and you will recognize it as soon as you play it. Here is the pattern:
1, 3, 5, 7
The reason it is called a major 7th is that it adds a major interval (four half-steps) to the root chord.
It can be especially effective at the end of a sad ballad. (I use it to end Over the Rainbow and Both Sides Now.) Here are two alternate endings using a G Major 7:
These are not what you would call traditional blue grass chords, but when you play them on a Dobro, especially if you pick the strings a little up the neck, say right between the sound holes, where you get those rich even-order harmonics like the notes are coming from a Les Paul through a vacuum tube amp--you will add some real mood to the right songs.
Now, let me go to the fridge and pour another glass of my cardboard-eaux (wine-in-a-box) and play like Josh wearing an ascot.