littlemagic - are you aiming to follow a specific plan? Because that will sort of dictate what you can/can't eat, as they will be based around different levels of carbs.
In essence, though, you can eat:
All meat, poultry, fish and seafood that is unprocessed
Some processed meats/fish - e.g. bacon, ham
Anything that isn't in its raw state has some kind of additive/process that will add carbs. Sausages, for example, can be incredibly high in carbs - so always check the labels on anything that isn't the meat/fish in its raw state
Most vegetables - especially salad and green veg
Fats
Low carb diets are mostly higher fat diets. You are allowed to eat:
butter
cheese
cream
olive oil (and all other oils)
You are also encouraged to eat fattier cuts of meat and can enjoy things like crispy chicken skin (yum!)
Some fruits - although not many (and none at all if you're doing a really restrictive low carb diet/phase, e.g. Atkins induction)
rhubarb (sweeten with Splenda rather than sugar)
berries (strawberries, blueberries, raspberries)
melon (in some cases - but can be too high in carbs)
If you're following Charles Clarke's High Protein Diet, he recommends an orange a day - but this would be too high in carbs for some other plans
The things you must cut out/avoid/restrict:
potatoes
bread
pasta
rice
flour
sugar
fruit (apart from the ones above)
alcohol is not easy to include (as with any other kind of diet) - this is not only because it contains carbs, but also because alcohol is the first 'fuel' that your body will burn, so whilst it's burning alcohol it's not burning fat.
The best advice I can give you is to read up on low carbing and decide which type of plan you want to follow.
These are all worth buying/borrowing:
Dr Atkins - The New Diet Revolution
India Knight/Neris Thomas - The Idiot Proof Diet
Charles Clarke - The High Protein Diet
Zoe Harcombe - The Harcombe Diet
But as Pag says, there are lots of low carb threads going - just jump in and join one. Even though they may be established threads, you will find that lots of us are re-starting as it's January!
Good luck