Lend out any high value items you have (In the norther part of the GE, World 2, members only) I usealy rent out my Saradom Sword for 350k for 12-16 hours. It takes about 15mins and is super easy.
Other items to lend out for a good profit are (but not limited to):
2)Any partyhat (if you had one you wouldn't be here though)
3)Any rares (santa/h'ween/other partyhats you have)
6)Staff of light
10)High end Dragon armor (chain/plate/full helm)
11)Dragon resource equipment (Pickaxe and hatchet)
12)Godwars dungeon armor (bandos and armadyle)
13)Dagonoth rings (berzerker/archer/seers)
14) Theres tons of others but in tired of listing them.