For low-volume e-commerce websites and other applications like support desk, contact forms etc we do recommend 256-bit PositiveSSL from Comodo. PositiveSSL is one of the most popular and inexpensive SSL certificates in the industry. This hassle-free certificate is the ideal choice for websites where the brand's trust is already established and organization verification is not needed.
RapidSSL from Geotust (subdivision of Symantec) is an ideal choice for securing new, small and medium-sized businesses and web pages with limited traffic. RapidSSL is an affordable, domain-validated certificate and is usually issued within minutes. It provides strong 256-bit encryption and comes with a free "Secured by RapidSSL” site seal.
We use both RapidSSLs and PositiveSSLs across WHM/cPanel, chats, supports desks etc for many years.
For billing applications we do recommend Thawte. Thawte SSL is a low-cost SSL solution. The certificate is very easy to install. Thawte validates your domain ownership before issuing the certificate. All Thawte SSL certificates include a free dynamic Thawte Trusted Site Seal and unlimited free reissues. Please note that it may take up to two business days for the cert to be issued.