Stilly, I echo what MMario said- Solanaceous members (potatoes, tomatoes, etc.) not only are all vulnerable to the same diseases and insect pests, they have very similar needs in terms of trace minerals, nutrients, etc. It's much better to not follow one with another for those reasons.

I find it difficult to effectively rotate crops effectively in a reliable way in a small garden, but by amending soil regularly, planting catch crops and cramming in cover crops wherever possible, we've managed with minimal rotation. I'd follow the tomatoes with a legume, say, and use the spuds in a new soil location. Potatoes are a good starter crop in new soil.

You'll figure it to suit your garden.