I won't go on about the ridiculousness of commercial room deodorizers and instead focus on how easy it is to make your own - and with a small kit of essential oils and a bit of sniff knowledge, you can literally have a home chest of smells for every occasion.
If you want your chosen essential oil blend to be balanced and to last, you need a mix of top, middle and base notes. While you sniff an overall blend when you have mixed a few essential oils together, there is actually an order to the way they emerge. What you smell in the first few minutes will not be the same as what you smell a half hour later.
Top Notes are the first you smell first when you breathe in a blend. This is because the are made of tiny, light molecules that evaporate quickly. These top note scents are often described as cheerful, bright, light, refreshing. Citrus oils fall into the category of top notes.
Middle notes give a blend their main body and you will recognise them because they are generally the most popular scents. Middle notes do not evaporate as quickly as top notes and stay around after the top notes have gone. Lavender is an example of a middle note.
Base notes have heavy molecules that are slower to emerge and take much longer to evaporate. Base notes add depth and richness to a blend as well as acting as an anchor for the blend. Sandalwood and Patchouli are both examples of base notes.
Ideally your essential oil blend for a spray, personal scent or diffuser, will contain a top, middle and base note, allowing for a balanced blend that is pleasing to the senses. The recommended ratio is 30:50:20 (Top:Middle:Base), so simply count your drops in this pattern.
Here is a list of common essential oils, with their note standing and a description of their scent from Complete Guide to Essential Oils on Wikibooks.