Installing quality pickups is the single biggest thing you can do to improve the sound of your guitar. After an upgrade, most people find that even a mid-grade import sounds as good as a custom shop guitar.
I sell Seymour Duncan, Mojotone, Kent Armstrong, LR Baggs, and K&K Sound pickups. Most sets are special orders that can be on hand in a week.
Modifying the electronics in your guitar is also a great way to open up new tonal possibilities. Options like coil-splitting, series/parallel switching, and tone cap swaps can turn a one trick pony into a jack of all trades.
Even upgrading the pots, switch, and jack can open up the tone like taking a blanket off off your guitar. I use only high-quality industry standard parts.
Electronics repairs/mods/etc. are billed at the standard hourly rate, with a 1/2 hr minimum.