Well, first off, the second Haruhi Light novel was released this month, so its worth picking up if you liked the first. Second of all Full Metal Panic had its first 3 main story novels released in english, but nothing ever since, which is annoying. You can still find the first two novels easily enough, however the third is generally out of print everywhere you look, but i'd recommend reading it if you want to what FMPs original content was like.
Spice and Wolf volume 1 is due out near the end of the year and despite its rather changed cover, i'd recommend giving it a go. Outwith the trade jargin its got good characters and character relationships, or rather, the one between Horo and Lawrence. Its like haruhi and FMP though in that its still ongoing.
They are the main ones that come to mind straight off, but i think there was a twelve kingdoms light novel series too. I would also say look into Moribito, but its not exactly a light novel, though its still worth a look into as its one i thoroughly enjoy.