XDCC Catcher is the most advanced download manager for XDCC bots. Its been under development since 2009, has more than 32000 lines of pure code and is available in a free Basic version and a paid (15 euro) Pro version.
Some of the features are :
If you're unfamiliar with IRC and/or XDCC, please read the chapter "Brief introduction to IRC and XDCC" in the XDCC Catcher Basic quick start.