This is an excellent question, and one I didn't really really pay attention to when I first pulled out my shovel.  I made the raised beds parallel to the slope with no drainage option, mostly because you want raised beds to be flat on top, and it's much easier to make them flat if you build parallel to the slope.

Since reading Eric's comment, I've been keeping my eye on the beds and I've been pleasantly surprised to see very little water building up in the aisles between.  Granted, it's been relatively dry here (you know, an average of only about half an inch of rain per week), so the groundwater isn't terribly high.  But my sky pond is still about halfway full, despite the fact that Lucy thought there was some kind of critter in the drainpipe from the roof and ripped it to shreds a couple of months ago, meaning only groundwater is recharging the pond.  (I really should fix that....)

Barring extreme waterlogging in my new gully beds, I figure I'll just plant with the water in mind.  For example, I discovered this summer that the watermelons planted in a raised bed above some very soggy soil did much better than those in the main part of the garden, so those would be a good choice for our chinampa beds.  And for all I know, next year will be as dry as this one was wet, and I'll be glad for every ounce of water retained.

Or maybe I'll change my mind and add some drainage!  Only time will tell.

By the way, I decided not to bore you with a full-blown advertising post, but did want to alert you to the new sale on our chicken waterer website --- I hope it makes your holiday shopping easier!  Cold weather has been keeping me inside, so I'm also making changes to my email lists --- please stay alert and click to confirm that you want to stay on my lists if you see an email from me in your inbox.  Thanks for bearing with the marketing interruptions!