Agree with moshie's list and would add geraniums to that, most thrive on neglect and will flower all summer. Shrubs are generally your best bet, if you have a good local garden centre or nursey then go and see what you like and ask for advice on what will grow well where you are (alkaline/acid soil etc, they will know which you have) and which things are the toughest. Also suggest getting a basic gardening book from the library, I found ther Matt James City Gardener books useful when I was starting out, they are all easy to follow and good for inspiration.
If fir trees and heather are happy in your garden, it's probably got acidic soil which is what mine is. The other big group of things which would be very happy in it are rhododenrons and azaleas - I have only managed to kill one out of about a dozen of those in my garden, so they are fairly safe. Like the term "herbicidal" - I think it describes my skills very well!