For now Crucial will offer 4 different types in their Ballistix series: PC3200, PC4000, PC2-4200 and PC2-5300. Each of those modules comes with a custom-designed aluminum heat spreader, dome decal case bage and decorative sticker.
Crucial Ballistix PC3200 (400MHz), CL2 2-2-6, currently priced at $74.99 for 256MB, and $138.99 for 512MB; Crucial Ballistix PC4000 (500MHz), CL2.5 4-4-8, currently priced at $77.99 for 256MB, and $144.99 for 512MB; Crucial Ballistix PC2-4200 (533MHz), CL3 3-3-10, currently priced at $118.99 for 256MB, and $228.99 for 512MB; Crucial Ballistix PC2-5300 (667MHz), CL4 4-4-10, currently priced at $124.99 for 256MB, and $238.99 for 512MB.Crucial is the second company after Corsair memory to start shipping DDR2 modules at 667MHz. The 667MHz DDR2 stick from Crucial has tighter timings : CL4 4-4-10 compared to CL4 4-4-12 on Corsair's side.
Source: X-bit Labs