MSAA- Has the same good points of FSAA, but without the blurring. This would have been part of Rampage too(so it should be quite a bit better then 3dfx's FSAA). With MSAA, you also have a comparitively tiny performance hit, no fillrate and roughly 50% or less of the bandwith for FSAA.
Pixel/Vertex shaders. There are a lot of truly cool effects that can be done using these. Now that DX8 has native support and the NV20 along with RadeonII have support we should see games that use some of these tweaks.
~Vertex Morphing- ATi's Radeon already has this, the NV20 will also. This could be really sweet for doing something like a person talking. Instead of a hinge for a jaw, people will look like they are actually talking.
Programmable T&L- This solves the only major gripe I have seen regarding current T&L, lack of flexibility. This, combined with the time T&L boards have had on the market(much larger installed base), should push developers to start supporting high geometry models for their games more often.
EMBM- No nVidia board to date has supported this, the NV20 will.
Volumetric Textures- Actual 3D textures, they don't require any polygons to be mapped to. Not sure exactly how popular they will be, but the concept sounds interesting at least.
Effective fillrate- While this is mainly a speed issue, it still will be nice to have ~1.5-2GTexel effective fillrate in 32bit color. 1600x1200 32bit could be over 100FPS in Quake3 with everything cranked(GF2U hits about 60 now).
Raw poly power- With the flexible geometry engine, and support for HOS, the NV20 should easily handle geometric jumps of an order of magnitude over even the best game in that aspect now(probably Giants).
500MHZ RAMDAC- While many will say this isn't needed, the issue that current nVidia boards have with 2D when paired with certain monitors should be gone. It is very possible that they may compete or best Matrox in 2D quality.
MPEG2 Decoding- The GF series of boards already offers some, and I'm not certain the NV20 will offer more, but MPEG2 acceleration is now part of DirectX so they may have a superior solution compared to what is currently available in video cards.
That's all I can think of, and of course almost of that is pure speculation(I'm not currently under any NDAs involving the NV20), but nVidia has said several times that they will have a fully compliant DX8 part so the features should be right, the performance is a best guess based on rumors and facts that we know about the chip right now.