Been using the Drake Sword as my primary weapon so far, but around level 37 now and it's starting to be ineffective. Recommendations for something to replace it with?
A weapon at +10 will outclass Drake Sword.
1) Find a weapon with a move set you like. Have you tried out any of the katanas like the Iaito (found in blighttown) or Uchigatana (kill the burg merchant)? The balder side sword, any halberds? Claymore? Clubs? These are just some weapons I like, there's tons, and they're all pretty viable when upgraded.
2) Obtain the minimum stats for using the weapon. From here you've got a bunch of options. Assuming it's a regular weapon you upgrade with titanite:
3) Upgrade to +5 [can do this right away]. From here you can make chaos or fire weapons in the Catacombs . Then max out chaos (+5) or fire (+10) path. [chaos ember / large flame ember needed]
OR
3) Upgrade to +10 [requires large ember]. From here you can make it a lightning weapon in Anor Londo. Then max out the lightning path (+5)
OR
3) Upgrade it to +15 [requires large ember, very large ember]. Use this option if you chose a weapon that scales well with a stat like STR or DEX. For example, demon's great machete scales well with strength, balder side sword scales with dex, etc. THEN level up the stat that the damage scales with. If you went with fire/chaos/lightning, don't go beyond the minimum requirements for the weapon as scaling won't be a factor anymore. A weapon with only C/D/E scaling (halberds, zweihander, etc) is probably better off as a chaos/lightning than +15.
Then, with a +15 weapon, enchant it with crystal magic weapon, darkmoon blade, or sunlight blade.
OR
3) If it's a weapon that uses twinkling titanite/demon titanite/dragon scales, upgrade it all the way and level up the stat it scales with. My favorite unique weapons: Chaos Blade, Moonlight Greatsword, Black Knight Great Axe