Vacuum. Squeeze a bit of fresh lime or lemon juice in your vacuum's bag before sweeping your carpet.
Extracts. Combine vanilla, almond, or other extract with a cup of water, and spritz with a spray bottle about your living space.
Vinegar. Simply place a bowl of vinegar in the living room, kitchen, bathroom, etc, and let it sit while you're away for a few hours. When you return, the vinegar smell will have gone away, taking other odors with it.
Vinegar #2. For particularly offensive smells, simmer white vinegar in a small saucepan on the stove for 30-45 minutes. As it evaporates, it will help dissipate other smells.
Citrus Zest.Don't even use or eat a piece of citrus without saving the zest, or rind (the peel, without the white 'pith'.) If there's no place for it in your recipe (though there probably is), simmer in a bit of water, or place in your garbage disposal and run for a minute with the hot water running.
Baking Soda. Read here for lots of ideas.
Lightbulbs. Add a drop of essential oil to a lightbulb ring, and add the ring to each lightbulb in a room. The heat will help it move throughout the space, and it's apparently fire safe.
Fabric Softener Sheets. Have a peek here for several techniques.
DIY Simmering Potpourri. Simply simmering several ingredients and spices does a great deal to scent your space. Look here for some excellent recipes.
Make your own paper air fresheners. Read this instructable to create a custom air freshner for use in your car, office, or locker.