Best scientific (not programmable, not producing plots) calculator in your opinion.

[rprosperi]

If you are limiting this to new models (i.e. still in production) you should look at the HP-35S. It is programmable, but of course there is no need to use the program features. While there is a lot of info on posts here (and many other places) about all the bugs this machine has, I believe they are mostly (all?) related to programming, so would not affect you.

The 35S is RPN (or Algebraic if you prefer) and is loaded with built-in functions including integration and a solver (related to, but can also be used independent of normal keystroke-programming).

If not limited to new machines, you can pick up a used HP-32S (similar to above, has programming, but no need to use it) for a reasonable price via auction sites, etc. The later 32SII does more (e.g. fractions) but typically will cost more as well.