You are at:
The end of the BWO's: May still be a few left, especially this year (as hatches are late), but they should be waning. Daytime hatch (somewhere between, oh, 10 a.m. and 4 p.m., depending on weather and so forth). Fish won't respond well if it's bright and sunny. Size 18ish.
March Browns: Not a traditional hatch on this stream, but the lower reaches (below Bellefonte) have been seeing them in the last few years, so the hatch may be recovering. Probably good timing for this one. Afternoon/early evening hatch, spinners fall right as it gets too dark to fish comfortably. Size 12ish.
Sulphers: Typically would be beginning the first week of May. Since hatches are late, you may be too early for this one, but I'd have a few on me just in case. Dinnertime or later hatch, spinners fall right as it gets too dark to fish comfortably. The early ones are size 14ish.
Other than midges and such, that's about it for the hatches, Spring isn't prolific with hatches. Nymphs of the above will work. And on spring creek, sowbugs are always a reasonable choice. If the water's up, sculpins are always a good choice as well.
This place is a good fly shop for supplies and the latest scoop on the fishing.
http://www.flyfishersparadise.com/
Good luck.