Check out the Ikea page for your local Ikea store. Each Ikea store runs itself slightly differently and has different offers on.
I live halfway between two stores, one of which was offering 2 hours free childcare in its creche if you booked in for one of its kitchen design slots. There is also an offer on at one of the stores for 20% off all ovens during September so we went there and got £70 off our cooker and then went to the other one to finally buy the rest of the kitchen.
I went to Ikea with my measurements for them to do an initial design during a 2 hour prebooked slot and then, because our kitchen was still being built, tweaked the design at home to suit my needs and the ever changing dimensions of the kitchen. I really like that you have the flexibility to do that at home. I took three trips into Ikea, on each occasion using the help of the incredibly friendly and useful staff (the last two times just on a drop in basis, rather than pre-booked), to finalise the design and buy it and I can honestly say the whole process was pretty enjoyable and pain free - the promise of icecream kept DD very happy throughout.
I also went to Howdens (on a Monday morning). They took my kitchen measurements and we had a discussion about what I wanted where but it took them until Friday afternoon to e-mail me with any pictures. I only had that one week off work to sort stuff out so they missed their chance there.
I didn't like that there is no breakdown of prices with Howdens, they will just give you an overall price. With Ikea, I liked that I could see that if I changed from unit with larder interior to one with just shelves, for example, it would save me, say, £63.
I just loved playing on the Ikea planner - let me come and design your kitchen for you - I'm sad that I've finally bought mine and have no excuse to play anymore!