A good signature will be brief, list your name, company name, what your business does and why it's better. Here's your chance to mention new products, or your newsletter. Keep it fresh so it captures your readers attention. Use your imagination, play with the characters on your keyboard. Try BizBot, Link Booster.
Most ads are free with upgrades available for a fee.
A hassle free guide to ezine advertising is The Directory of Ezines. Offer a free teleclass to visitors. Ask them if they'd teach a teleclass with you. Renting a telebridge is pretty inexpensive. This is a powerful tool for attract potential customers.