The most popular (probably because of its superior quality and reliability) brand for dev. device on GBA/SP has dropped significantely its prices for his all range of product. The perfect time to buy is now!
Heres more info if you dont know what it is:
Overview of the product
A 2Gig cartridge compatible with the Flash 2 Advance ULTRA, the most popular and top quality back up/development unit for Gameboy Advance. The biggest cartridge on the market with 2G MEMORY! IMPORTANT: Requires a F2A USB or Parallel linker to function.
Specifications & extra information
Product Features:
Built-in Real Time Clock and Real Time Save functions.
SRAM size inside the Cart has been significantly increased to 8M.
100% compatible with all the saving functions with today's GBA
Available to directly play Pokemon Ruby and Pokemon Sapphire with 100% hardware compatibility
Using Japan-made ASIC to independently design and produce the mask