Are you going to include a drainer or not? Either way if your budget allows I would buy Franke or Blanco. I have had (and currently have both) but prefer Blanco. Lusso stone also does stunning composite sinks. It depends on your budget. I think some of the larger DIY stores sell them too. Whichever kitchen supplier is doing your kitchen should have a list of suppliers for you to choose from. It also depends on what material you choose and whether it is undermounted or a belfast style.

No Drainer - just the double.

The size of the sink will also depend on the size of the sink unit, if you're after a double bowl sink then the base unit will need to be at least 800 wide, but if you mean a 1 1/2 bowl then it should fit in a 600 base. There's plenty of sites on line that have sinks [google is your friend] and when you look at the sinks it will say the minimum size unit it will fit in.

One other thing to watch out for is the position of your tap and the tap style, with single leaver taps the handle has to move back as well as forward, with a double bowl sink it can position the tap hole quite far back ie closer to the wall or upstand which can effect the operation of the tap. You can of course then spin the tap round so the handle is at the front, but if its a hot tap then you may not be able to do this.