Here's some more we use... again not favourites so much as house rules we like. Note we play RM Classic.
Character Law (ChL):
House Rule ChL1: Linear Power Points (PP) vs Stats (steps become 1, 1.5, 2, 2.5, 3, 3.5, 4 on Table 02-02, p.31)
House Rule ChL2: When rolling to increase Hits for Body Development, may reroll 1's
House Rule ChL3: "Extended Stat Gains", Optional Rule 5.1 from RMC4.
Arms Law (AL):
House Rule AL1: For Initiative, use 2d20 (2-40) instead of 2d10 (2-20).
House Rule AL2: Melee attack vs non-melee combatant resolved at Activity midpoint. If midpoint is 50%, it is resolved in Phase 1.