Make sure that you have your own website up and running before you attempt to start selling your product. Any attempts at marketing your CD may well be wasted if you're unable to direct potential customers to a site where they can find details about you and your music, and subsequently decide if it's something they'd like to buy.
Sign up with PayPal (see Resources) and set up a shopping cart on your website so you have the option of selling directly to the consumer. You'll be responsible for buying mailing supplies, tracking orders and shipping, but you'll be side-stepping consignment fees. Other than small PayPal transaction fees, your costs will be minimal and the profits will be all yours.
Sign up with a third-party retailer in a non-exclusive agreement. CD Baby is probably the most well-known, and for good reason. For a one-time fee, the company sets you up with a page where you can post descriptions and reviews of your CD, as well as hosting 2-minute clips of songs of your choosing so that potential customers can sample your music before buying. CD Baby also takes care of all payments and shipping of your product in exchange for a $4 fee per unit sold. As an added bonus, the company can deliver MP3s of your tracks to most major digital download sites, including iTunes, which saves you a lot of legwork.
Spend some time on social networking sites, especially those that offer players that feature your music. Even if you don't have a lot of time to spend on the sites, having a page with your bio and sound samples on it can only help your visibility. You'll get random visitors to these pages, so make sure they're linked to your own website. Of course, the more work you put into promoting your pages, the more results you can expect.
Be active on genre-specific music forums. Joining in conversations with like-minded individuals is a good way to introduce your music to new and sympathetic listeners. Make sure that your online signature includes an active link to your website and online store, so that every time you post, people will have an opportunity to visit your sites. Try not to shamelessly spam the members of forums with blanket emails; rather, try to add something worthwhile to discussions. You'll garner more respect this way, and quite possibly, a few CD sales.