Keap is one of the most robust, but also quite pricey. There is Zoho and SalesForce. But, it really depends on your company needs. Customerhub (though more powerful when bundled with Keap / Infusionsoft) is another solution, but with much less features and tools.
Also, aMember is one that requires a one-time purchase. Not as fancy with the bells and whistles that the others have, but usable for many companies.