House Sparrows are in massive decline - I remember seeing a program about it on TV once, so you will be doing good by feeding them.
I'd suggest loose seed somewhere high up but sheltered so it doesn't all blow away, and where no cats can get to them, if you are able to set such a thing up. Sparrows will eat things like bags of nuts and those fat feeders, but seem to more readily eat the seed.
Quote:
The House Sparrow's diet is diverse: seeds, nuts, berries, buds, insects and scraps, etc.
The House Sparrow will eat just about anything: sunflower hearts, high energy seed, peanuts, suet, kitchen scraps, etc. In fact, as reported in the BTO's Garden Birdwatch Handbook, research in the 1940 found 838 different types of food in the dissected stomachs of house sparrows.
from
http://www.garden-birds.co.uk/birds/housesparrow.htm