A photo of the singer or band is always useful on an album cover as it helps potential buyers identify the product. Famous examples include "Thriller," Michael Jackson's sixth studio album, with Jackson reposing in a white suit and black shirt. With a digital camera, you can take hundreds of photos of the artist, then choose the best photo to feature as the album artwork.
A photo of an iconic building is an eye-catching choice for an album cover, especially if you process and edit the photo imaginatively -- it can be a reference point in the real world being used in a creative way. Pink Floyd's "Animals" is a good example, featuring a broodingly atmospheric image of Battersea Power Station, with a pig floating between the chimneys. Use photo-editing software to access thousands of options for photo processing.
A fantasy world, like the one featured on Meat Loaf's "Bat Out Of Hell" can make a striking album cover. Here, a flying motorcycle, driven by a prone rider, is shown having emerged from a graveyard, while an open-winged, giant bat in the background bares its teeth. If you can draw or paint and have some imagination, create artwork that relates to the songs on the album or the album title so people have a sense of the music inside the cover.
An abstract design on your album cover is often an attention grabber, as people try to work out what the artwork is all about. Whether you decide to relate the work to the music on the album or take your imagination in another direction, you can produce work that has a strong identity. Don't necessarily choose your first idea. One idea might lead to a better one. Sketch out a few options, leave them for a while, then go back and pick the strongest one to work on further.