I'm going to start with a disclaimer here...I am a distributor for Groten Molen mills through my business
http://www.grainsandmore.com.
That said, if you are looking for a mill that will grind flours but not nuts and seeds your two best bets, in my opinion, are the K-Tec or the Groten Molen Wondermill. The K-Tec is less expensive, noisier and a little messier to deal with. Both work very well, have enclosed burrs that are guaranteed for a long time and give you control of the grind from fine to coarser. They cannot grind nuts and seeds because the oils will destroy the mechanism.
If you want a mill that you can use to grind seeds and nuts, think nut butters, in addition to grinding grains from fine to cracked your best bet is the Groten Molen Wonder Junior. It is a hand mill and does an amazing job. Very easy to clean. A bit pricey though. The next best choice, in my opinion, is the Country Living Mill but it is a lot pricer and I think it's harder to clean but it works very well. For an inexpensive-ish hand mill the Back to Basics mill is a good choice.
A coffee grinder works well for flax seeds but if you're trying to do nuts or larger seeds or grains you will wear it out very quickly. The add-ons for a Kitchen-Aid type appliance will also burn out the motor quicker if you use them to grind grains.
Hope this helps.