Flouradix .. get it from a health food shop, take a spoon before breakfast and one before dinner .. it will take a month or so but has no nasty side effects like constipation (which you get with iron tablets)
as for diet .. red meats, green leafy vegetables and drink something with vitamin C at the same time (as it helps absorption) .. orange juice is good, so is cranberry juice
there is a FAB thing called Spa-tone which you can buy in boots.
It is basically little sachets of this incredibly iron-rich water. tastes vile on its own, but mix it in with a bit of juice and it's fine.
The midwife recommended it to me because you absorb it much more easily than the iron in tablets because it is in water form so you get more iron from one sachet than you do from taking tablets.
It also doesn't cause constipation or any of the other nasty side effects of tablets!
twiglett is right about the vit C, but also avoid dairy products just before and after you take any iron products because it stops absorption.