I would like to second the Sliquid Organics lubricants, particularly the 'gel' variety. I've tried a number of water-based lubricants, and many of them irritate me. Sliquid Sassy Booty, for example, always causes me discomfort, but the Sliquid Organics Gel did not (I believe I had the one with carrageenan). It still washes off in water, of course, but the gel is a little more tenacious because of its viscosity.

Something more waterproof would be a silicone lubricant, but those aren't generally good for silicone toys' integrity. It's a shame, really. I've heard that higher quality silicone lubes won't damage high quality silicone toys, but I'm too scared to risk it, even after having the lube pass a patch test.