Ramp (blue)
Ramp is about accelerating land deployment and/or mana access. Blue isn't great at this, though there are a few options. Apprentice Wizard grants 3 colorless mana for the cost of 1 blue. Lapis Orb and Midnight Clock are mana rocks with a bonus ability. Guidelight Optimizer, Volshe Tideturner, and Vodalian Arcanist are 'conditional' mana rocks, granting access to mana but only for certain spell types.Card draw (blue)
Blue excels at card draw. There are many options here . . . below is just a smattering. Many options (Mind Spring, Concentrate, Divination) are simple card draw spells; others (like Merfolk Looter) grant a card at a cost of a discard. Still others (Deduce, Consider, Opt) offer card draw with a bonus ability of investigate, surveil, or scry. Spectral Sailor is a great option, paying dividends especially in later stages of a game (when you could potentially activate his card draw ability several times).
Targeted removal (blue)
There are two ways blue does removal: counterspells and returning a permanent to its owners hand. For counterspells: the original (and still best) is Counterspell. That was deemed too powerful at only two mana, so subsequent iterations either kept the cost and added conditions (Mana Leak, Essence Scatter, Negate, Disdainful Stroke), added a colorless mana to the cost (Refute—note the card draw bonus, Cancel), or added two colorless mana (Rewind) but you get the lands back to use again that turn.
For returning permanents, Boomerang and Disperse are classic options. Fading Hope is a nice conditional variant, Blink of an Eye has a nice kicker bonus, Run Away Together can synergize well in "ETB" decks, and Aethersnipe can grant you a creature, too.
Board wipe (blue)
Similar to targeted removal, blue does board wipes by returning permanents to their respective owners' hands. Wash Out is great against mono-colored decks, Aetherize goes well against aggro offerings, Whelming Wave if you're playing sea creatures, and Upheaval if you just want to reset the board.
Conclusion
Of the 32 cards presented above, ~24 of them go well in almost any mono-blue Commander deck.