hi ahquan,
I'm a beginner to DSLR photography, but for your wide angle solution I would like to recommend that you take a look at the
Tokina AT-X 116 PRO DX (11-16mm f2.8) as well.
Yes, it can't focus on D40X but manual focus on this lens is really easy. I tried it out at a camera store today and found MF really quite a no-brainer on this lens, even though I've almost never used manual focusing before. It was actually quite fun to MF on this Tokina because it's so simple. I think it's because it's a wide angle. I almost bought it actually, but settled on something else instead based on my current "needs".
Check out Ken Rockwell's rocking review of this lens too:
http://kenrockwell.com/tokina/11-16mm.htm
I'm not sure about the pricing, but I think it's great value for money, given the superb image quality and truly wide focal range (for APS-C size sensor), plus its solid build quality too. (I highly prefer it to Sigma's EX finish, which peels off over time. I've actually seen demo Sigma lenses in the store that are slightly peeling after some wear and tear.) I'm not sure about the pricing in Singapore but it's selling for as low as 57k yen where I am now.
Anyway, happy lens hunting!