I sold my Minix fairly recently (good mobo, but I stopped using the HTPC). With a 45W TDP CPU, it should run very efficiently. Keep in mind that the TDP is just a vague approximation for the processor series' max possible power usage. For example, some those Core 2 CPU's you mentioned that have a TDP of 65W will actually run at around 30W max.
Anyway, you didn't seem to mention this, but I assume that you want a mini-ITX system? If you're OK with mATX, you open up a lot of possibilites. The options you have with mini-ITX are quite limited if you want a good IGP. The Minix would probably be your best bet, in that case, at least at a fairly reasonable price. Otherwise, you can go with a 780G or better AMD system, or maybe a low-power (e.g., E5200) C2D system with onboard GeForce 9300 or 9400.
Hope that helps a little!
EDIT: I just did a quick search... If you want mini-ITX, maybe something like
THIS may not be bad. Just stick in an E5200 or something like that.