We just got a new kitchen as part of our house extension, so the whole layout had to be designed from scratch rather than just replacing an existing kitchen IYKWIM so some of this may not be appropriate for you but:
We went to about 5 or 5 different kitchen shops and got them to design a layout and then took the best bits of each design and then went somewhere else. Bit cheeky perhaps but we're really pleased with the results. Harvey Jones were really good even though we were never going to buy a kitchen from there as
at the £££s (but they don't give you the plan until you sign up, so we went straight to a coffee shop afterwards and sketched it out again while we could remember it)
Get lots of pan drawers for storing everything - they're fab
We have two corner cupboards, one has a carousel and one has "le-mans" mechanism. The carousel is much better, stores way more stuff.
Think about where you are going to store everything before finalising your design. I worked out exactly what was going to go in every drawer & cupboard at the design stage. For example all the plates and cutlery is stored next to the dishwasher so it's really to put everything away. I have all the baking stuff close to each other (scales, measuring jugs, rolling pins etc). Chopping boards near to where the knives are. It gives me great joy that it all works so well 
In our island we have an intergrated (sp?) bin with different sections for rubbish, recyling, compost. I love that when I've finished chopping I can just pull out the bin and sweep all the waste in the compost
We got slightly deeper than standard worktops. The extra space is brill, means I can keep the breadmaker and food processor on the worktop all the time and I use them much more as a result.
If you are having underfloor heating (ace BTW) make sure you don't have it under the bin