The NTG-2 and NTG-1 are the same mic, but the NTG-2 can supply its own phantom power via an internal battery. The same applies to to the AT875 and AT897. The biggest difference between the mics is that the self phantom powered mics (NTG-2 & AT897) appear to have lower volume output levels; pair that with the DR-40, DR-100 or H4n, which have lower input volume levels, and you have serious volume level problems (the DR-100MkII, which is due out in the spring, reportedly has resolved the problems of the original DR-100 -
news at 11:00 
). Personally I would get one of the "true" entry level recorders like the FR2, PMD-661 or the HD-P2. Yes, I'm aware that these are all currently out of your price range.
The "sound" of various mics is another subjective topic and can be quite vociferous. The $500 ME-66 is a decent mic, but to my ears is on the brittle side. The $700 NTG-3 is, IMHO, a substantially better mic, and has been called the "poor mans" MKH-416 ($1,000). When you get to that level of investment you need to weigh your options carefully. No matter what, I'm sure that the ME-66 will sound much better than whatever it is you have currently.
So my advice would be to get the NTG-1 or AT897 and a couple of battery packs for the DR-40, which would come to about the same price. The reason for the battery packs is that budget recorders go through batteries at a ferocious rate when supplying phantom power. In the long run you'll save money if you think about the cost of going through a sleeve of batteries every shooting day.
No matter what, the techniques used make even more of a difference than the equipment. Great boom technique will more than make up for using budget gear, but crappy technique with even the best gear will still yield crappy sound.
A final bit of advice - opinions are like a$$holes; everybody has one and they all stink! Do some serious research and come to your own decision.