I have the Downey 4" lift springs on my 40. They are fairly inexpensive and I have no complaints. Also, take into consideration everything else you'll need to replace/add along with the springs: Extended brake lines, shims, U bolts, shackles, bushings, shocks. If you don't need the full 4 inches of lift, the OME 2.5" kit comes highly recommended by a lot people. Kurt at Cruiser Outfitters usually has a good price on the kit.
'73 FJ40 - '85 FJ60 - '05 Tundra