Switching PSU and residual noise on the rails
You have to consider the frequency of the noise you want to get rid of. This is very important.


LF noise/ripple, like below 1 kHz, or 100Hz ripple.


Do you actually need to get rid of it? Most likely your opamps have 100dB PSRR in that frequency range so they don't care. Also most linear regulators have very good PSRR at low frequencies, so they will clean up your supply just fine. You can even use a switcher to get rid of LF ripple, but you get more HF noise in exchange of course.


Medium frequency, like the 20k to 500kHz sawtooth at the output of your DC-DC or AC-DC switching converter. 


As frequency gets higher, most regulators and LDOs begin to suck in the PSRR repartment, and the opamps you power too, so this is the part when you need to look at datasheets in greater detail. Some regulators have pretty good rejection in this range, others are abysmal, especially the micropower ones, which are optimized for low idle current, and thus have rather slow control loops.


HF noise like a converter's switching glitches.


This will go straight through most regulators and opamps.

The best way to handle the last two is the good old RLC filter. 

Usually, in this application, ferrite beads are better than inductors. They use a lossy core material which allows them to turn into resistors at HF. Also they usually have less interwinding capacitance than an inductor (ie, less HF goes straight through). Murata lets you download spice models, so you can play with them in simulation.

So, you select a ferrite bead based on DC current (do not saturate it, or it loses its inductance), its inductance value (for low frequency filtering) and its high frequency impedance (for HF filtering). Or course higher inductance/impedance in the same package lowers the saturation current, so size and price matters.

Then you put a capacitor after it. Its value depends on the frequency of the noise you want to attenuate, of course. This is, after all, a standard LC lowpass filter, so its cutoff frequency should be properly placed...

Noise around 20-100 kHz is a bit problematic, because frequency is high enough to make the PSRR of your regulator suck, but low enough to require annoyingly large L and C values. Good choice of parts is important there.

On the other hand, and this is a bit of a paradox, switching noise at 1MHz is much easier to get rid of, since your LC filter has more frequency to work with. The ferrite bead will have a much higher impedance, and a small ceramic cap works wonders.

For HF noise like switching spikes, it's all about layout and ESL.