The gear isn't what will make your songs sound good, it's you, however some high quality gear can be a ton of fun to play with and has the potential do some very cool things. If you want to pick up a really solid midi controller that will let you chop samples, program drums to pads,
effects to knobs, and all of your sounds to a 2 octave keyboard check out
the Akai MPK-25, especially the variant with the MPC pads. For being such a lightweight and
compact keyboard you get a tremendous amount out of it, and never any latency or detection problems with any DAW. I've used M-Audio midi's for years, and although great, find they don't always sync up well with some DAW's, as they do others. Akai, on the other hand, has been the king of making sampling equipment since the early days of beat making.
For monitors, if you're doing this at home, just buy a fat set of Rokits and don't look back, my personal opinion however.