End grain to long grain glued joints are not very strong, and in most cases a form of reinforcement is required.
Biscuits are more for alignment than for strengthening joints. They work well in long grain to long grain joints (e.g. joining planks to make a table top), but not so well in end grain to long grain joints (e.g. rails meeting stiles). In reality the glue is doing most of the heavy lifting, the biscuit is simply providing a convenient way to line the work pieces up.
Pocket Hole Joint
A pocket hole joint provides strength without the use of glue, though it does not provide a clean fastener-less appearance. It is a very popular joint since it's strong, versatile, and easy to create.
While dowel joints might take a bit more effort to create, they are very useful for adding strength to almost any joint.
Mortise and Tenon
A mortise and tenon joint provides a very strong joint, which is especially true for end grain to long grain joints. The design of the joint actually changes the joint from an end grain to long grain joint, to a long grain to long grain joint.
If it were my project I'd use either dowel joints, or the classic mortise and tenon. If I didn't care about having a fastener-less appearance, I might use pocket hole joints in some places to speed up the building process. My biscuit joiner, however, would never leave the shelf during this project.