Here's a pack of about 80 transitions I made for RMXP. They're pretty simple, and just are gradients with gimp filters applied to them.
https://www.box.com/s/j46l15k2ual61s0c7su7 (https://www.box.com/s/j46l15k2ual61s0c7su7)
And some examples of the cooler ones:
(http://i.imgur.com/J21excH.png)
(http://i.imgur.com/S04DHtQ.png)
(http://i.imgur.com/WdsRGpq.png)
(http://i.imgur.com/LT77Y3e.png)
(http://i.imgur.com/GpnKfTy.png)