Using "F":
* Fabulous Friday
* Fresh Friday
* Festive Friday
* Fancy Friday
* Fun Friday
Using other letters:
* Sunshine Friday
* Radiant Friday
* Wonderful Friday
* Glorious Friday
You can also get creative with your alliterations:
* Five Friends For Friday Fun
* Fun Friday Feast
The best alliteration for you will depend on the context and the feeling you want to evoke.