The cheapest fix though not really recommended for an old spring set are spring spacers. You would normally get this for a new suspension lift that doesn't fit level or after a year or two when one or more springs settle faster than the rest.
__________________ '03 TJ Sport / D30/Ford9 / 35x12.5x15 KM2 / D window black steel 15x8 wheels / 3" custom long arm lift / SYE & 1350 DS / JKS BL / 1" MML / Smittybilt's front bumper, Tube fenders, Rocker guards, and rear bumper / High Rock Tire Carrier
Wranglers put a lot of force on the right rear spring during acceleration. There are a lot of them going down the road with a slight tilt. Usually it is on Jeeps a little older than yours. You can do like suggested above and get a spacer to level the right side or swap in another spring.
98 Sport Red 5spd
RC 2.5 lift/Daystar 1in BL/BrownDog 1 in MM/4.88 Yukon gears/Ford 8.8 rear/Spartan lockers/RC stabilizer/JKS quicker discos/FabFour Hardcore Bumper/SB XRC8 winch
Cragar 365 series V5's/35x12.50 BFG MT KM2/Grant Tire carrier bumper
I noticed last night, mine is the same way. I actually measured the springs as well, and sure enough the passenger side, front spring is about 1/2" shorter (or more compressed) than driver side. Rear had a small difference, but it was pretty negligible, maybe 1/8" high on driver side.
Planning to upgrade my lift in the relatively near future anyway though, so not too worried about it.