After onions?

I am thinking about next year's plot plan and wonder what to plant in the bed where the onions/garlic/shallots will be after they have been harvested.  My leeks will follow the potatoes and I have a separate bed for winter brassicas.  Is there something which folks generally put in after onions? Or would it be better simply to dig over and prepare the soil for the following year? All suggestions welcome.

I follow onions with quick leafy crops as Gavin suggests - salad leaves, oriental greens - plus I usually stick in chard and/or perpetual spinach for an early spring crop.   I use pelleted chicken manure for a quick nitrogen boost to the soil on planting and again in the spring to get the chard and perpetual spinach woken up after the winter.

The last 2 usually bolt as soon as the spring warms up, so I dig them out then, dig in some compost and am ready for replanting with something else late spring or early summer 

My  :dry:autumn planted onions came out reasonably early due to the hot weather we had, I've sown some autumn king carrots, spinach, turnips and radishes direct and also a few kale seedlings. There goin to be on the smaller side but it beats nothing

I've manured where my Onions have been and will plant Potatoes next year. You could plant some green manure over winter if you didn't want to leave the soil bare.

After garlic(which is out early July) I put in winter brassica plants grown in pots (to the 5 leaf stage), such as cabbage and Purp. sprouting broc.  These finish in about April and I follow with squash.

For the onion bed, I mulch straight after harvest, then sow Wizard field beans beginning of October.
These produce green pods from June, then we let most mature until harvest in September and store as a dried bean over winter, sprouting, boiling and using as a dog food suppliment. The bed is mulched heavily and left over winter from Sept. until sweet corn goes in in May.

I am with Ema.  Autumn planted onions if they've done pretty well can come out by July.  Then in with something as a transplant.  Dwarf beans, runner beans are good even if you have another sowing way ahead as they freeze so well once blanched.  Using root trainers for the beans you can get a really decent size plant that transplants really well.

A sowing of beetroot is also good.

My autumn onions are out by mid June!! Start them as green onions on 1st may and by mid June they're finished. Then start on the main crop..