raised-bed Raised beds and plant spacing

What is everyone's recommendation for spacing between pepper plants when growing in raised beds? I'll be growing mostly chinense with a few annuums, baccatums and pubes, somewhere around 40 plants total.

It seems like the general recommendation is 18-24 inches. I'd love to go with 18 inches since I don't have unlimited space and could have more plants with the tighter spacing. I'm not sure if I'd regret not going with 24 though after they are fully mature.

I've previously only grown in containers so I didn't worry about this as much since I could always move them around but now I am planning to build some raised beds and plant spacing will affect the bed size.

My beds will be at least 12" deep, maybe 18" with open bottoms (no barrier between the added raised bed soil and the natural soil beneath). Each bed will have 2 rows of plants. If I go with 18" spacing between plants I'll do 3 feet wide beds and if I go with 24" spacing I'll do 4 feet wide beds but will have to have fewer beds.
Look up Joyner's square foot garden and see how closely you can actually pack the Chinense and what they look like at the end of the year. He can really grow some nice big plants in a small space. Personally, I'm around 2' for chinense and pubes and 16-18" for all the others.
Last year I put my plants too close, 12-16 inches apart.  24-30 inches is  is my plan for this next years crop.  I have raised beds that are 4'x8'.  I will be putting 8 plants (instead of 16) in each, 4 in each row with 2 rows.
It's not a big deal if you want more plants in a smaller place, except that the tallest plants get more sun and do better than the smaller ones, and you have to water everyday and feed more often when you have that many in a small space.  I also had trouble getting to all the plants to inspect and harvest easily.
Good luck!  
This past summer I made a 20' x 5' x 13" (well no bottom really) and planted the square foot way the entire bed. Huge mistake. My plants in the bed reached just over 6' and it was a jungle and a mess. It was so hard trying to climb into the middle of the jungle and harvest pods without breaking plants and knocking off unripe pods. Then trying to read the markers at the base of each plant. I had the plants 5 deep. Maybe if I had done 3 deep it wouldn't have been so bad. Probably what I'll do next year in that bed.
Im planning 4x6 beds.  Will be putting 12 chinense in one planted 3 rows of 4 plants with 12" spacing from the bed wall for each outer row and the middle row will be planted dead center.  In another bed I am going to only plant 6 Baccatum's because I understand they get big and bushy and need cages. 
I've got two 8' x 3' x 18" raised beds.  I space the plants about 16" apart on the X axis, and offset each plant by about 6" on the Y axis (shown below).  This has worked out pretty well for me.  The plants don't get too crowded, and it's easy to maintain and harvest pods.  Two years ago I grew 18 plants (3 rows of 6) and it was way too crowded.  It became a pain to water (I don't use a drip system), and some of the plants over crowded others and blocked sun, and total pain to pick pods.
I use a similar system to Turbo's in my 4' x 10' raised beds, with a total of 14 plants per bed.
x          x          x          x          x
      x          x          x          x
x          x          x          x          x
Is what it looks like.  Plants are spaced roughly 18-20" apart.  Be sure to read up on each plants habitat though; I planted the Onza Amarillo seeds that Hogleg gifted to me last year and the plant grew 5' tall!  A plant that big on the wrong side of your bed will shade the others.  
I use the staggered method like Smoken Fire, but only two rows in my 4 foot x 32 foot bed, 16-18 inches apart.
                            (NORTH) (fence)
(WEST)  X     X     X     X     X     X     X  (EAST)
                  X     X     X     X     X    X     X.... and so on.
I did not find this spacing really affected growth, but, it is a major pain when harvesting, because my plants tended to grow into each other, making it difficult to reach some of the lower branches in the back (up against a privacy fence).
JoynersHotPeppers said:
First year I did a 4 x 4 with 16 plants.

They did OK
They're certainly healthy!
But I suspect you'd wind up with the same total plant mass with a wide range of individual plants.
There's only so much sun and so much soil to share.
Geonerd said:
They're certainly healthy!
But I suspect you'd wind up with the same total plant mass with a wide range of individual plants.
There's only so much sun and so much soil to share.
Actually the harvest from those far surpassed the same variety that had much more room. This is a 7 Pod White, picked a few hundred pods from it.