I'd recommend first reading Aaron Ross' - Predictable Revenue before choosing your CRM system.
Flexible and complete solutions I'd recommend
Hubspot CRM + Sidekick
Feel free to contact me for a quick chat about it.
We've built this for our SaaS business at Keywee. Let's setup a call.
All of the anwers here are correct. As a sales manager with 3 years experience I also recommend you to go with Hubspot + Sidekick solution.
I am also a founder of CEO of inbound marketing and Hubsport partner certified agency Incredo
We have 3 SAAS venture backed clients which use also Hubspot + Sidekick solution for leads nurturing and sales tracking.
Call me for strategic consultation and set up guidance
We have a number of early-stage and venture-backed startups we setup on Infusionsoft or IBM Silverpop (Engage). In most cases we can offer you better deals than if you buy from the company direct. PM me for details