The usual. Heroics, crafted items, and rep rewards will get geared you up for 25 man pretty quickly. You'll be hit capped, have decent unbuffed spellpower (1600-1700), crit, and haste before you ever step into a 25 man raid. The down side is that 10 man loot will be a lot less exciting.
Here's the checklist or pre-Naxx gear I made for my 'lock. It's silly to make a checklist, I know, but I got tired of wasting time looking through loot tables online. It took me just over 40 heroic runs to win drops, get the rep, and get the badges for this gear. Got lucky on some (only had to do UP once to get the belt) and was unlucky on others (lost multiple rolls on the UK ring).
http://i253.photobucket.com/albums/hh74/TomServoGAF/Pre-NaxxGear.jpg
EDIT: You can swap some of those around for other badge rewards or crafted items. Ebonweave gloves and robe have a nice amount of +hit which would let you swap out the UP belt for the badge belt, for example.