Most mastering engineers (myself included) DON'T use studio monitors. We use premuim and/or audiophile level HiFi type monitoring. I have a set of studio monitors here for use as a quick reference only.
The "real world" won't be listening on studio monitors - They're not made to sound "good" - they're made to be "accurate" which normally translates to "flat" sounding.
You need to find monitors that are able to give a relatively accurate response, but with fidelity that studio monitors aren't going to give. The acoustics in your room will be of paramount importance, along with your monitoring and amplification.
You will be the last line before replication - If something sneaks past your monitors, your room and you, it's permanent.
Let me put it this way (DISCLAIMER: I'm in no way trivializing the gear or the job of the tracking and mixing engineer, this is just the way things work with me, and with most as far as I can tell)...
I can track on just about anything I'm familiar with monitor-wise. When mixing, I need a little something extra - I'll *flip* to small monitors, but I need something with at least an 8" woofer. Genelecs, BX8's, 824's, something like that. For mastering, I need to hear everything on the type of gear that is meant to be listened to. The choice can be very personal. You need to use monitors that can reproduce sound well along and beyond the listening spectrum AND sound really great TO YOU.
I have a long story (that I won't bore you with) on my B&W journey. However, on my way to my current M-802's (these are my absolute dream speaker - I wouldn't trade them for any other speaker, regardless of price, period.) I ran into the B&W 602's. They're what I would call an "entry level audiophile" speaker. They sound fantastic, detailed, "creamy" (Blue Bear's words on the tweeter), and at $600 a pair, they are well less than one-tenth of the cost of a set of the current model N-802's. And of course, the Wharfedale Diamond series - The best bang-for-the-buck there is, IMHO. Nearly as wonderful as the B&W 602's, at half the price again at around $300 a pair.
Both the B&W 600's AND the Wharfedale Diamonds have floor-standing models also, which I would HIGHLY recommend if the $$$ are available. You can set them up on cinder blocks (I use wooden mission cubes with 70 pound concrete slabs on top) to get them to near-perfect ear level.
With either of these, it's a completely different listening experience than you would have with a standard studio monitor. It takes practice (and a lot of it) to get used to the sound and to be comfortable with them. I would suggest two albums - Pink Floyd "Dark Side of the Moon" and especially Steely Dan "Aja" - Play the hell out of both of them. On Aja, listen to the detail in the highs - The triangle on the title track - The tight bass - The absolutely stunning amount of ultra-high-end that doesn't sound the least bit irritating.
Okay, I'm rambling now - Lots to do today. Be back later.