Well for starters, if it's 3,5, LN isn't allowed by RAW. the players handbook version is LG only, but unearthed arcane has builds for CG, LE and CE paladins. But lets imagine your GM has allowed it and you are using the base ph paladin.

First of, you need to decide what type of paladin you want to be. There are plenty of good builds, like mounted with a lance, dual wielder, power attacker (2 handed wpn), sword+shield, etc. each has their benefits, and you should determine this first, as it decides what items you should get. As for items, i personally use a book called Magic Item Compendium A LOT. I lists a lot of items in, IMO, a better way than other books.

Base items;

A magical armor. depending on what your GM will allow, a +1 armor with something like light foritification (25% chance for immunity to criticals) or some other +1 effect is a good thing (a +2 armor is +4k, so 5.65k for a full plate). But if you browse through magic item compendium there are some cool effects like glamered (can disguise the armor as clothing) or blueshine (acid immunity and bonus on hide, metal armors only).

A shield if applicable. Again, +1 with some +1 effect. if you want to bash, the bashing enchant is powerful (the shield counts as 2 sizes bigger, so spiked heavy shield deals 2d6 damage pr. hit). cost for a +2 shield is also +4k (so 4180 for a spiked heavy steel shield)

One or two magical weapons. you will need a basic magical melee weapon. but depending on what you want to do (like a mounted paladin or a paladin with a bow or dual wielding), 2 may be a good choice. 2 +1 weapons is 2k each (+base cost). a +2 is 8k.

Armor+shield+2 weapons is about 18k (depending on what items you pick) and that leaves some gold for adventuring items (holy symbol, clothing, tools and such). That is 9k left over for wonderous items and material components (I don't recall if paladins use materials for their spells)

As for what wonderous items you should take, it really depends on how you want to play, and which books you are allowed to take, but in magic item compendium there is an item called "Battle bridle" which is a saddle that boost mounted abilites (p. 151 if you want to look for yourself). If you reply some information of your ideas, i might be able to dig up some interesting items. If nothing else, boost your cha with a clock of charisma (cha is a very important stat for paladins)