OP: The best value overall is the Sony MDR-7506. It leans towards neutral - and is generally the best tracking/monitor phone for professional use available(but this does not mean it may be best for general listening use to everyone). Build quality here is exceptional. Ear pads need replacing every 2-4 years, depending on frequency of use.
The Grado 325i you mentioned is on another level over the Grado 60, 80 and 125. The 325i is superior in sound quality and build quality, by a substantial degree. Based on SQ, I would pick the 325i over the Sony 7506, probably. But you should be warned that Grados are considered uncomfortable by an unusually large number of people - so that could always end up being an issue even if you like them otherwise.
If you prefer jazz, classical and other acoustic type music, you may be better of to consider Sennheiser HD580 or HD600(same headphone frame and transducer - different color and exterior grill), which should be found for very good prices. However, especially with classical music(which is recorded at a low level to allow large dynamics), the HD580/600 may not be suitable to most portable audio devices without the aid of an additional amplifier to boost the voltage level.
Another option is the AKG K271 Studio. It also needs an amp in the same conditions as the Sennheiser HD580. However, the K271 is closed, providing much sound isolation. It is rather large in size, if this is an issue.
-Chris