Mana Ramp for White and Blue?
White and Blue don't have much in the way of mana ramp. However, since you're looking at everything but Vintage, you do have some options:

White cards dealing with land tend towards restoring balance, and as such there are several card which can only get you land if an opponent has more already.


Knight of the White Orchid
Kor Cartographer
Oath of Lieges
Planar Birth (if you can dump lands into your graveyard)


Blue can, of course, steal land. It also has several card which cheat permanents into play, and happen to include land as an option.


Annex (in addition to many other cards which can steal any kind of permanent)
Arbiter of the Ideal
Braids, Conjurer Adept
Dreamscape Artist (this is Harrow, both color shifted and turned into a spellshaper at the same time; Planar Chaos be wacky)
Eternal Dominion (of course, you don't need mana for casting spells afterwards, but you could still use mana for activating abilities)
Show and Tell


In addition to adding more land to the battlefield, you can get more mileage out of your lands. "Twiddle" effects are fairly common in blue, and Urza block had a slew of creatures and spells which would untap the same number of lands as their own mana cost, making the spell very nearly free, or if you had lands that tap for more than one mana, you could get more mana than you otherwise would have had.


Cloud of Faeries
Frantic Search
Great Whale
Palinchron
Peregrine Drake
Reset
Rewind
Snap
Time Spiral
Treachery
Turnabout


You can also reduce your costs; you don't actually have more mana, but you can do more with the mana you have. (Affinity for Artifacts in particular is on many Blue cards.)


Arcane Melee
Ballyrush Banneret
Council of the Absolute
Daru Warchief
Etherium Sculptor
Grand Arbiter Agustin IV
Herald of War
Hero of Iroas
Mistform Warchief
Stonybrook Banneret
Stormscape Familiar
Sunscape Familiar
Warden of Evos Isle


Finally, artifacts can do all of the above, from putting land onto the battlefield (Burnished Hart, Explorers Scope), to tapping for mana (Sol Ring, Darksteel Ingot), to making your lands tap for more mana (Gauntlet of Power, Caged Sun), to reducing costs (Cloud Key, Helm of Awakening), and even Twiddle effects (Candelabra of Tawnos, Sword of Feast and Famine).

It ought to be obvious, but this answer is by no means an exhaustive listing of your options. You're not going to vomit a deck full of lands onto the table playing a White/Blue deck, but there are still ways for you to get ahead in the game.