Ranger Modification

[Geiger Counter]

I want a ranger that casts and gains spells like a beguiler or warmage.
What spells should I put on it's list?

[tuesdayscoming]

It may not be quite what you're looking for, but have you looked at the feat Sword of the Arcane Order from Champions of Valor? Lets you use your ranger spell slots for wizard spells. You just have to have access to a spellbook with the spells you want to memorize.

It does have a couple of faction based prerequisites, but you might be able to talk your DM into modifying them.

[Biffoniacus_Furiou]

There's the Mystic Ranger (http://crystalkeep.com/d20/rules/DnD3.5Index-Classes-Base.pdf) variant (page 91), which gets an amazing spellcasting progression in exchange for delaying most of its other class features.

As tuesdayscoming said, the Sword of the Arcane Order feat from Champions of Valor lets you prepare Wizard spells from a spellbook in your Ranger spell slots. This can be combined with Mystic Ranger to get access to the next level of spells just as fast as a Sorcerer, though only up to 5th level spells.

There's also the Prestige Ranger (http://www.d20srd.org/srd/variant/classes/prestigiousCharacterClasses.htm#prestigeRanger), which could be combined with something like Cleric, Archivist, or Favored Soul to get higher-level spellcasting with Ranger abilities.

If you mean you want to cast your spells spontaneously, maybe get your DM to try out the Spell Points (http://www.d20srd.org/srd/variant/magic/spellPoints.htm) system from UA. You get your normal number of prepared spells, and those which you have prepared are your choices for what you can spend your spell points to cast.