Ultra overclock(290-300+) = G.Skill PC4800 (also the CAS 2 version, the 2X512 TCCD ones... GBLA I think...), OCZ PC4800 Platinum
Medium overclock(251-289) = Corsair PC4400 TCCD, G.skill PC4400 TCCD (GBLE maybe.), OCZ PC4400, OCZ PC3200 Platinum Rev. 2's.
Medium low overclock (225-250) = OCZ VX 4000, Mushkin Redline PC4000
Stock speed = OCZ PC3200 Platinum Rev, 2's... Any CAS 2 ram... Corsair Valueram... for budget. yeah.
If you can get g.skill... you got the best ones you can find for dfi. the ultra overclockers though.