http://www.foodstandards.gov.uk/news/newsarchi ve/2004/jun/fishportionslifestagechart link to FSA site that should help - lists types of fish and amounts to consume...
Also you may find the info at:
http://www.seafish.org/plate/details.asp?catid =4 link to the healthy eating fish recipes at the Seafish Authority site useful - lots of suggestions about things like mackerel, etc.
You'll see most oily classed fish are the sort of fish you will have to do something to before eating, but salmon of course is nice, mackerel as mentioned readily available to eat without cooking further, fresh tuna, eg a tuna steak - is in the category too - takes 30 secs to cook on a griddle per side - and so are anchovie - best to get the whole fish and simply grill, but a few dozen fillets on a pizza might do?!!
Hope this helps...