By "rebuildable", I'm guessing you mean the coils can be replaced with pre-made factory-built coils? There's many options available, so here are a few which have been on the market for a few months and appear to be consistant performers:
Aspire CE5, mini-nova, vivi-nova. These all use the same dual-bottom-coil head which is replaceable. Filled from the bottom; coil replaced from the bottom.
Innokin iClear 16 and 30s. These are dual-top-coil which are replaceable. Each model has its own coil head replacement, so they are not intercompatible between models. Filled from the top, coils replaced from the bottom.
Kanger Protank-2, mini Protank-2, T3S, and Evod. These are all single-bottom-coil and the coil heads are intercompatible. The Protank-3 and mini Protank-3 is now a dual-bottom-coil and the heads are not compatible with the above. Filled from the bottom, coils replaced from the bottom.
Go to
YouTube, and do a search for each make and model to see review/demos.