Here is a bunch of ideas I get from time to time.
Sometimes I try to make them myself but most of the time just better to hope someone more experienced does it.
01 - A Title screen for Final Fantasy III (Famicom/Nes English Patched)
02 - Final Fantasy II USA with the Final Fantasy IV title screen imported directly from IV (Famicom), Like the patch that is on here that changes the Final Fantasy III USA's title screen into Final Fantasy VI's.
I also saw a patch on here that converts Earthbound's Title screen into Mother 2.
03 - A fully translated Dracula II - The Accursed Seal for Famicom Disk System.
I heard there was one going under way but haven't heard anything since.
04 - Metroid II - Return Of Samus ported to the NES.
05 - Super Metroid's title screen converted into Metroid III.
06 - Metroid Fusion's title screen converted into Metroid IV.
07 - Metroid Zero Mission's title screen converted into simply Metroid.
08 - A patch that converts the english Earthbound Zero's title screen back to Mother.
09 - Bowser replacing Wart in Super Mario Bros. 2 (Nes)
10 - Super Smash Bros for the NES.
11 - A utility to edit Castlevania IV's maps like Stake and Revamp are used for Castlevania I and III.
12 - A patch that puts the VRC6 music into the American Castlevania III.
13 - Play as the Shredder in TMNT I for Nes.
14 - Be able to select all characters and maps in TMNT Tournament Fighters (Genesis)
Still upsets me to see in the instruction manual player 1 as Triceriton. What a tease.
15 - Oh oh, Here's my favorite for last, A patch that converts the gore factors back into Castlevania IV USA.
Like the blood on stage 8 instead of slime. All the naked statues and such. Etc.