Nothing until the soil warms up (and dries out). You're a bit further north than me, but I reckon to be getting potatoes in from early March, so you could be buying them now and setting them to chit. And peas & broad beans can go in early as well.
It really depends on: a) what your site is like (My advice here is to go round and ask questions and keep an eye on what everyone else is doing & when.); b) whether you have a greenhouse or cold frame, in which case you can sow things a week or two early, ready for planting out later; c) what the weather is going to be like this year.
