damnit skotekal! i was gunna say that! :]
ok, the elenium. same author, different world.
there are the elder gods and the younger gods of the Styrics, and the God of the Elenes. Set in a roughly medieval time frame, with magic very dissimilar to the belgariad. Focuses on the church knight Sparhawk, the church knights fight for the church of God, but know some of the arts of the styrics (magic). exciting world with ogre, trolls, undead, demonic things, and good old fashioned human selfishness and treachery. as well as thegood guys of course. im gr8 at these summary things, aint i?
Animorphs: K. A. Applegate.
bit of oldish 1, possibly out of print, certainly can't get in your local W H Smiths nemore! Save the world, invading aliens, more aimed at teens or young adult that a proper full on novel, if you like could finish one (or even 2) books within a day. self contained but continuous, can pick up any of the books and read, but best of read from 1 - 56(?).
The yeerks are invading, not the whole ZAP! TSEW! etc. of laser fire, but stealthy, gradual. you see, the yeerks are parasites. they live in your brain...
The Demonata : Darren Shan
still in print this 1

meant as a horror book series but i dont find that scary, still a good read. seperate universe (but still based in our own) from his 'saga of darren shan' vampire series.
and, i havent read it, but i may as well mention it, to go with the elenium in the same way as the malloreon goes with the belgariad; the Tamuli.