Romi's Sprite Tool 1.41 will be in SMWCentral in September 9th, 2011.
It will be in progress in August 29th, 2011.
Here's My Suggestions:
A Hoopster From SMB2 (it's GFX will be added in Mario2(SP4).bin and it will use Palette E).
A Stalking Pirahna Plant From NSMBWii (It will use Palette C for head and D for stalking vine Just like the Venus Fire TrapFrom SMB3)(It's stalking vine GFX will be added in SP4)
You can now copy sprites and custom sprites lists from SMW hacks For Example (Brutal Mario) using Sprite Crop.
You can now create a custom sprites from other games for the SNES with Sprite Creator (Just savestate while facing a boss and standing at enemies only at 2D Games, NOT PLAYERS, AND RPG GAMES!!! then, just use the sprite you want, Last It will be in SMW.

What's Yours?: