First, NEVER shoot TIFF, only JPEG or RAW.

With the D100 only RAW gives you the best quality in terms of sharpness and detail. I assume the D70 would be similar. JPEGS tend to be soft, only god knows why since the 10D outputs JPEGS that are identical to RAW files.

Anyway, 512 meg cards, best price/performance ratio, and they keep you from putting all your eggs in one basket.

512 meg cards with my D100s:
150 Jpegs, highest quality
50 RAW
1,500 JPEGS lowest quality, lowest resolution

Can you imagine losing more images than that if a card or reader fail? I use 5 512 meg cards.