Here in the western U.S., it's still considered early spring. The temperature today will only reach 50 degrees F, so it's a little early for above ground crops... But, if you're in the same boat temperature wise, you can still plant root crops, such as carrots, beats and onions (from sets). Wait until the soil temperature reaches at least 50 degrees, preferably 60 degrees F before planting any tender, above ground crops, such as lettuce and don't plant anything from sets such as cabbage, tomatos, or cucumbers until it warms. Now's a good time to weed the area and work in some mulch such as peat or composted cow manure though. Best of luck!
At present, garden centres have young vegetable plugs, if you buy these, thats a fairly easy way to start, but again, it all depends on your ground preparation, A very easy one from seed, is Leaf Beet, called Perpetual Spinach, tastes just like Spinach, and is so called, because when you take a leaf off, another grows in its place, there are others, but, if you don't have a Greenhouse, i'd stay with the plugs.
if you are in the good old UK, try radishes, spuds, lettuce,spring onions and beetroot. They are all real easy cos its what i used to grow. you can put carrotts next to the sping onions too to stop carrot fly