90 Degree Phase shift at few MHz
If you are happy with feeding a signal into a "block" and getting two signals out that are 90 degrees apart may I recommend this: -



Select R = R1 = R2 = \$\sqrt{\frac{L}{C}}\$. This ensures that OUT1 and OUT2 have a phase differential of 90 degrees across all frequencies. The phase relationship between OUT1 and OUT2 is always 90 degrees but amplitudes do change with frequency as with any high-pass or low-pass fliter.