RapidSSL is dirt cheap.. but it doesn't have great name recognition. If it's for an online store I'd go for something more upmarket like Thawte, Verisign or GeoTrust. It will pay for itself thanks to the trust it generates and they have a whole heap of different pricing points.
If the data you are trying to protect is highly secure than go for 265 bit keys, other wise 128 should be the minimum you'd go for.
i used to buy direct but now i just pay hostgator $50 for the cert + $24 for an IP per year and they do it all, thus i don't have to muck around with anything.
http://www.cheapssl.com - resells them all - I don't know who owns them but they are cheap as.. Also - one thing to remember you need to have a domain setup for the domain you are actually getting the ssl for, or access to the registrar domain to action this, but apart from that it's quick, cost effective and works.