I'm going to start by say that I've never been a fan of the spell slot magic system. "Vancian" magic has always seemed like the "wrong" way of doing magic, but that's just my opinion. Since paizo has decided to dig in deep with vancian magic (every new book being dominated by new caster options), I've had to like elsewhere for ways to be cool and use magic. the the 3 systems I present are as follows: Psionics Updated and rereleased by Dreamscarred Press, psionics provides a flexible system much like traditional magic. The major difference being that it skews spell slots in favor of a single pool of points that can be spent to cast any spell known to the caster An over view can be found here, <a href="http://www.d20pfsrd.com/psionics-unleashed" rel="nofollow">http://www.d20pfsrd.com/psionics-unleashed</a> Pact Magic This one is a real treat from Radiance House Press. Pact Magic is a masterfully redone system based on the system by the same name from d&d 3.5. Pact Magic is a system where you bind daily spirits to your very soul in exchange for powers and abilities. An overview of the system in its newest form can be found here, <a href="http://spheresofpower.wikidot.com/pact-magic" rel="nofollow">http://spheresofpower.wikidot.com/pact-magic</a> Spheres of Power By far the most interesting and difficult to apply to a standard game. Presented by Drop Dead Studios, spheres of power is the most fat removed system from traditional magic. That said, it provides an unprecedented level of flexibility to those that use it. <a href="http://spheresofpower.wikidot.com/" rel="nofollow">http://spheresofpower.wikidot.com/</a>