Legumes are a huge part of Tim Ferriss's "slow carb" diet. He has mentioned that he thinks they are excellent for fat loss (especially lentils... though he's not quite sure on the mechanisms).

What's funny is Robb Wolf did a guest post on paleo on the 4HWW blog and this topic came up. Here is Tim's response:

"Many of you know that I consume some legumes and beans. Normal cooking will reduce anti-nutrients in both, but, when possible, I also soak them overnight beforehand in water with a tablespoon of baking soda. Soaking for 24 hours at room temperature has been shown to remove 66% of the trypsin (protease) inhibitor activity in mung bean, 93% in lentil (this is what I eat most often), 59% in chickpea, and 100% in broad bean. Remember also to distinguish "in vitro" (e.g. red blood cells in a petri dish) vs. "in vivo" (e.g. after normal digestion) studies.]"

http://www.fourhourworkweek.com/blog/2010/09/19/paleo-diet-solution/

I would probably go with lentils and peas. I actually still love me some peas once in awhile. The last time I ate beans I had some black bean soup and it was a disaster. I was curled up on my side all night with painful gas. Never again. Luckily, I never really had a thing for beans. They fell in the category of "good for me and they don't repulse me, so I'll eat them" along with oatmeal and whole grain bread. The only legume I miss is whatever hummus is made of. Oh god, I used to down tubs and tubs of that stuff.

First answer, none.

Second, if I was determined to eat lectin-harborers I'd do an elimination diet and slowly 'try' different types and see which, if any, had any negative effects, in addition to soaking and cooking well.

I'm not as versed in their composition as many others so I can't get into technicalities. Imanomnivore seems to have done a sufficient post on them though.

Skinless urad dal is very low in lectins, phytates, and other irritants. It also ferments very well as idlis. It is literally the only legume that doesn't give me embarrassing stomach issues.

Green beans, snow peas, and anasazi beans all are low in lectins.

I don't avoid them, but I try to stick with ones I've grown myself, so that mostly means peas, lima beans, and various shelled beans. They're easy to grow and harvest and store (dried), come in assorted sizes and colors so they look nice, and (like potatoes) they're tasty eaten with a lot of fat: refried beans with lard, ham and beans, boiled limas slathered in butter. Of course, they aren't a daily thing in our diet -- maybe weekly -- and I always soak dried ones overnight. I wouldn't try to make them a daily staple just in case there are still anti-nutrient issues. (But then I'm not sure anything should be a daily staple, except maybe meat.)