Lenovo X-series are great for a full-featured laptop in a miniature package - X201 is probably the best mix of high performance and small size out there, but the battery life is not comparable to a netbook or other lower-performing ultraportables (Core 2 ULV-based). HP also makes a similar, but rather chunkier, 12.1" i3/i5 notebook; I've only used it in-store but it seemed OK just not worth the money when the pricing was nearly identical to the X201.

Those use the regular i3/i5/i7 mobile versions. There are substantially lower-clocked and more battery-friendly ULV (ultra-low-voltage) versions although the i5 and i7 versions will reach higher speesd temporarily or when operating primarily on one core, with the "Turbo Boost" feature. There are not yet many notebooks using the new i5 ULV-version processors; when those become more common there should be a lot more options. Right now, the two models I'm aware of using these are the Acer TimelineX 1830T (the i3UM version is best avoided because of the lack of turbo boost) and the Dell Alienware m11x. I'd expect more of these soon.

If you need more power than a netbook, but don't need a full-powered processor, there are quite a few consumer-ULV (CULV) and business ultraportables using various Pentium Dual Core (SU4100) and Core 2 Duo ULV (SU7300 at the low end, SU9600 at the high) The new Macbook Air 11" is one such example, as are the Acer 1810T, Dell Inspiron 11z, Latitude D4200, etc. These are going to be a good bit slower than a regular Core 2 Laptop (and unlike the new ULV i5s, no useful turbo feature for occasional higher speed on demand) but are WAY faster than single-core netbook processors. The "Core 2 Solo" SU3500 is best avoided; it's not much faster than a netbook Atom processor.

There are also a few netbooks based on the dual-core Atom D510 and D525 processors (intended for nettop atoms) and on AMD Neo X2 processors (also dual core) - these should be much better than single core Atoms (N270/280/450/475) but with worse battery life; I haven't seen enough benchmarks or used them to really compare them fairly to the CULV Core2/Pentium Dual Core but among the more attractive designs and prices is the Lenovo X100e (the Dell m101z is similar but a much less attractive design.) Passmark is far from my favorite benchmark, but the AMD in the Dell (about 750) and Lenovo (about 850) is bit low disappointing compared to the Pentium Dual Core SU4100 used in the older Dell 11z and Acer 1810T (about 950).

One other option for battery life is to go with a conventional laptop with an extended battery; it used to be possible with many models to swap out the optical drive for a 2nd battery - I'm not aware of any model that still allows it that, but quite a few business-line models have some other secondary-battery mechanism (for example, a "slice" which fits under the machine on some Dell models.) This tends to remain quite compact, but adds a good bit in weight, so it's not a good choice for those who are weight-sensitive.