Getting a little late for garlic, they need a cold snap to get them to divide properly.
As Juggerling says potatoes are a good first crop. Grow carrots and onions together they deter each other's pests. Carrot fly also homes in on the smell so when you pull out the thinnings to keep the ones you're growing on, do it on a damp day.
Now the important thing the taste!
Some vegtables are nice home grown and some are spectacular the ones that I think are particularly special are sweetcorn, peas and carrots (high sugar content basically) get them from the plant to the pan as soon as possible, within an hour or two if possible and you'll think you've discoverred a new vegetable.
There are a couple of good magazines on the market
http://www.kitchengarden.co.uk/
and
http://www.growfruitandveg.co.uk/
And they often have free seeds this time of year too