The "What Knife Should I Get?" Sticky
You may notice there is a paradigm in play here: 9" to 10" in length, 4 to 6 oz. in weight, and straight/tapered handles that are roughly as wide as they are thick. Generally, anything within those confines will flip well (unless the balance is way off), while anything outside the paradigm will take some getting used to (at best).
"CCC'S": $5 - $50. This is an acronym for 'Charming Chinese Cheapy,' or 'Crappy Chinese Copy,' or something similar. Generally not recommended, because of durability/safety issues, as well as ethical issues stemming from copies of well-respected makers, but it's better than nothing. Retailers often give them names on their websites, however the knives themselves are generally unbranded. These come in 2 varieties:
Channel style, zamak handles. Because the handles are made from cast low-quality zamak, they are brittle and break easily. They are usually held together with peened pins.
Sandwich style, steel handles. The handles are made from steel, but they tend to be thin and fairly flexible, which can cause the blade to stall at the worst times. This can lead to nasty cuts, even when performing what would otherwise be pretty safe maneuvers. Also, the screws are made from soft steel with odd-sized heads, and tend to fall out and/or strip fairly easily. Many of these also have a single cylindrical spacer on each handle, which is unstable.
Notable CCC's:
Jaguar Classic: $20 - $30. Clones of the old Pacific Cutlery 259. Channel-style zymak, they're very bulky, which makes them more difficult to break than similar CCC's.
MTech Twist: $25 Chinese clones (somewhat licensed) of the CKK Typhoon 'Twister' variant. They do flip well, due to their design, and their steel handles are much thicker than most CCC's. They still suffer from the same crappy screw problems as the other CCC's do, but these can now be easily replaced with better hardware.
Update: The availability of these has been spotty in recent years, with clones of their own popping up.
Also be aware that the 'Twsit II' is NOT really a Twist II. It is an old DDR Venturi Clone, renamed to 'Twist II' by certain retailers when the supply of MTech Twists was depleted.
BM4x clones: $30 Clones of the Benchmade 4x series. With channel-style steel handles, they are very durable. However, they are held together with typical CCC pivots, which can fall apart, strip, or wear out easy, though these can be easily replaced with better hardware.
There are also cheaper sandwich-style variants being made, but these have only a cylindrical spacer on each handle, which makes them far less durable than the channel variants.
Production Knives:
Bear MGC 114: $30. Featuring channel-style zamak handles bulky enough to withstand abuse better than CCC's of the same variety, decent blade steel, and (near) idiot-proof pin construction. They also make a model 113, which is basically the same thing, but shorter than the standard bali length. Other Bear models are pretty much more of the same, with upgraded cosmetic features that don't really improve durability or flipping quality.
Bradley Kimura series: $90. Well made, great pocket knife, fair flipper. It's relatively heavy, and the overall thickness of the handles is pretty thin (they're not as boxy as most). This can be good or bad for flipping, and currently it seems very subjective. They all pretty much flip the same - the differences between them are mostly cosmetic.
The K1 variants (now unavailable) had grooved handles. The K2 through K4 have handles skeletonized with small holes, while the K5 through K7 are skeletonized with long slots.
K1, K2, and K5 have spear-point blades.
K3 and K6 have tanto blades.
K 4 and K7 have bowie blades.
Bear OPS B200: $90. Great flipper, makes a great pocket knife. Fit & finish may be a little rough. Handles are sandwich construction, made of solid G-10. Blade is 154cm. There is also a trainer version of this knife available.
Bear OPS B400: $85. Same as above, but with aluminum handles and 14c28n blade steel.
Spyderco Smallfly: $125. A small variant of the Spyderfly (long discontinued). Not the best flipper, due to it's size, but a good pocket knife.
Benchmade 32 Morpho: $150. A great pocket knife, but perhaps not the best flipper, due to it being so short.
CKK American Patriot Kit: $175 Kit version of DRT American Patriot Balisong (see below)
Benchmade 51: $180. The 51 is basically a full-sized 32 - sandwich construction with liners and scales, as opposed to the 4x's solid titanium channel handles, and D2 blade steel, as opposed to 154cm. They are also lighter than the 4x's were, weighing in at only 3.3oz. Reviews are mixed, with 3.3oz being too light for some but okay for others.
Spyderco Szabofly: $220. A very unique knife. Perhaps not the best flipper, due to its odd-shaped handles.
Bradly Mayhem: $220. An excellent pocket knife, but perhaps not the best flipper, due to its odd-shaped handles.
Microtech Tachyon II: $280 A blast from the past, but longer than the original. Should be an excellent flipper.
Benchmade 6x: $290 Visually similar to the 4x series, but with zen-pin sandwich construction and shorter steel handles. Reviews are mixed, but they are considerably heavy (6.4oz) and pricey.
DRT American Patriot: $295 A.K.A. "the Wafflesong."
BRS AB: $370 Technically more small run than regular production. There aren't very many of these available, but reports are very positive.
FHM's: ~$150. Short for 'Filipino Hand Made.' A broad category, but these generally tend to be large and durable, with carbon steel blades, and with pinned handles made of brass and exotic wood or bone.
'Customs' and small-run productions: $400 and up. Some customs are truly made-to-order custom jobs, while the term is also used for small-run production knives, which are still a pain to make and therefore still costly. Many custom knives nowadays are made with either bushings or IKBS bearing systems installed, which make them the smoothest flippers around. The price range on these really have no limit, as you can have one made out of platinum if you really wanted.
Now discontinued: The following have been discontinued since this post was originally typed.
Benchmade 4x: $180 The 'x' is replaced with a number representing the blade profile - the handles are generally all the same. The most common is the 42 (aka BM42), with a 'Weehawk' profile. Other models are less common, and therefore generally more expensive. These are widely considered the best production flippers available.
They can be found used for about $350.
CKK Typhoon and Tsunami: $50 to $80. These are kits knives that, when assembled and modified properly, can make for an excellent quality flipper and a good all around knife. However, when assembled improperly and without the necessary modifications, they will lead to headaches, and therefore I generally don't recommend them to absolute beginners. The easiest to make into a good flipper is the Twister variant (now discontinued) , followed by the milled variant, followed by the solid variant, while the solid variant has the greatest potential for customization.
"NBO's": Near Balisong Object or Non-Balisong Object. These are items that can be flipped like a butterfly knife, but with the blades replaced by some other useful object.
Spyderco Baliyo: $10 to $25. A Fisher Space Pen. Plastic construction with brass weights.
BBbarfly: $20 to $30 A bottle opener with customizable graphics.
Bottlefly: $10 A bottle opener. Shorter and lighter than the BBbarfly.