Traditionally, assistants of all sorts are among the most "underappreciated" group of employees. In fact, this perception is so common that many assistants - virtual and otherwise - start out from their very first day of work bemoaning the fact that they are unrecognized and unappreciated. The hard facts of life are that this may be true, and it is unlikely to change much except during administrative assistants' appreciation week. However, in order to succeed as an admin, you must learn to get past this and not let it impact your daily attitude. If you can learn to "dole it out," then you will soon find that the level of appreciation for your work rises correspondingly to how appreciative you are of other people.
This can take some very basic forms. Whenever you speak to someone on the phone, thank them for calling (even if they are being obnoxious and you and your employer could not possibly care less about what they have to say!). This contributes to a positive perception of you and your employer, and will make future calls - and call screenings - run more smoothly. Also, be sure to thank people for their hard work whenever you send them any type of request. For example, if you need a document reviewed by another member of the team, when you send it, close with a "thank you for your time and effort" line that will let them know you appreciate the time that they are putting into getting this done for you. These types of closings will lead to a noticeable decrease in turnaround time for projects.
In addition to simple thank-you's, once a year show your employer some appreciation for providing you with a job. This generally takes the form of a traditional holiday greeting and perhaps a small gift. Simply thanking an employer for the opportunity to work for them can lead to a positive and growing relationship between you and your boss. This is particularly important for VA's, who tend to inspire less emotional loyalty than assistants who are physically present. By your virtual nature, you will always be easier to "let go" than someone who is right there in the office. As a result, you need to fortify your relationship with an employer via showing appreciation for them as well as by doing a great job in the role that you serve.