Almost any of the major brands of DDR2-667 will easily O/C to DDR2-700 speeds. Some of the DDR2-533 might hit DDR2-700 with extra voltage and relaxed timings.
For example, the OCZ Value series PC2-4200 is rated 4-4-4-12, but OCZ can handle fairly high voltage, so running 2.0 to 2.1v and using 5-5-5-12 timings will probably O/C pretty good.
How much are you looking at for capacity, something like 2X512? Are you looking for super cheap regardless of timings? If you are looking for RAM under $50, then you are probably stuck with 2X256, unless you can push the budget up to about $80 or so (Mushkin or Corsair).