OK. I'll play.
Lots to choose from, especially with the avalanche of Chinese mics now on the market (Rode, ADK and Avantone seem pretty consistent, although I'm not enamored of many of the other brands out there). It also depends on how you are using the mic and whether you are, performing, recording live or in a studio. It is worthwhile looking for used microphones on e-bay, Gearslutz, MusicGoRound and the Yard Sale. There are also many discontinued microphones that are excellent and which should be considered. I am generally going to list mics that I am familiar with by the major manufacturers and which can be found new or used for under $500 or so.
For inexpensive dynamic mics, I'd start with the ubiquitous Shure SM57 for instruments and SM58 for vocals. Typically used for either performance or close micing in the studio. About $100 each new last I looked. I like the Audix versions better for vocals myself (OM6 and OM7 - $220-230 new). The Telefunken M80 is also a good, albeit hotter, mic of this type. The Audix i5 isn't bad for a dynamic instrument mic (about $100 new). The Beyer M201 is also good for a dynamic instrument mic.
For better, but still inexpensive, dynamic mics for studio work, I really, really like the EV RE20 and Shure SM7b mics. New, they are about $350-450 and you can find them used for $300 or so. Terrific for vocals for many vocalists (Michael Jackson and Stevie Wonder among others). The RE-20 is also a really great live sax mic as well. These are originally broadcast mics and are really great all purpose recording mics, although you do need some preamp gain for them. Mine have been borrowed so much for recording that I now have 3 SM7s and haven't seen my RE20 in a couple years. Other considerations for better dynamic mics, especially for vocals, include the Beyer M88 and the Sennheiser MD431 and 441. The discontinued Beyer M500, which is a ribbon, can also be a great vocal mic on the right voice.
If your students want to troll e-bay, the EV RE10, RE11, RE15, RE16 and RE18 are also very good dynamic mics (good enough for Frank Sinatra) and can often be found for pretty cheap. I believe all are discontinued except for the RE16, which is a vocal mic.
For Small Diaphragm mics, there are the usual suspects we all know and love including the Oktava, AKG 460 and 480, and the Beyer MC 910, 930 and 950. I also like the Audio Technica line which IMHO is under appreciated. The AT 4041 is priced very reasonably new at @ $300 or so ($500 for a pair). The AT 4049 (omni), 4051 (card) and 4053 (hyper) are better and can often be found used for @$250-300 each (capsules can be swapped, the bodies are the same). The Shure KSM 141 dual pattern mic is also very good for the price ($400 new). It is worth looking for discontinued mic lines such as the Beyer MC800 and 700 lines with the changeable capsules. These are scarce, but do turn up from time to time (there is a pair for sale in the Yard Sale currently).
For LD condenser mics, better performing vocal mics in the $500-700 new range would include the Neumann KMS105, Audix VX10, Audio Technica AE5400 and Sennheiser e965. Obviously, these can be used in the studio as well, especially if the singer wants to hold the mic. Again, these can often be found on e-bay for substantially less, often in the $350 range (except for Neumann).
The AKG C535eb condenser mic is a good vocal condenser mic that also works well on instruments and is $300 new and @$160 used. Well worth considering if the better vocal condensers are too spendy. The Audio Technica AE5100 is also a very good instrument LD mic for close micing ($280 new).
For LD multi-pattern mics, AKG C414 (in all its permutations - used $500-600), AT 4050 (used @$400). Rode, ADK, Avantone and Blue have all made some very decent mics in this category and there are a huge number of other Chinese mics in this category as well. There are often cardioid only versions of the same mics available (or at least similar models like the AT4033 and 4047) like the Beyer MC 834 (the more expensive multi-pattern is the MC 740).
Older Groove Tubes mics can be very decent. The really old ones (Models MD1, MD2 and MD3) are arguably the best, were made in the US and can still be $500 or more. The Chinese manufactured models (in concert with Alesis and M Audio) were often decent as they had higher QA than many of the other Chinese manufactured mics of the time. In particular, I liked the AM40/GT44 Medium Diaphragm tube mic. At one point GC was blowing these out for $200. They originally listed for @ $600 if I remember correctly. Worth buying if you run across one and the price is right. There was also a FET version AM30/GT33 which was decent but not spectacular. In any event better than the overhyped AKG C1000s of the era (although I understand the new ones are better). There were also a number of Chinese manufactured GT LD mics, including multi-pattern mics that were decent and which should be a bargain now.
We could include ribbons too, but I don't know if you plan to go there. A lot more of those around now as well.