I'm thinking of purchasing a new immersion blender as a gift for somebody that has a very old one which is quite literally being held together with duct tape.  I own a Sunbeam model which I believe is rather cheap (it was actually a gift to me several years ago) and although I use it infrequently, I haven't had any major problems with it.  My internet research on immersion blenders hasn't uncovered much other than a few unverified statements that molecular cooks prefer the Braun models for foams.  No explanation of why, and I haven't even seen a Braun in any store here, but regardless, the intended recipient of this doesn't make foams, she primarily uses it (often) to make creamy soups and maybe a few other purée-based dishes.  I seem to be seeing the same Cuisinart model everywhere and am starting to wonder if I should just get that one and not bother looking for anything more... premium.  Are there actually any characteristics or features that make some immersion blenders better than others, either in general or for a specific purpose?  If so, what are they?  Also, I'm not necessarily looking for a recommendation, but a few times in the past I've been told to look for features which were apparently unobtainable, so if there are any unique/premium features I should be on the lookout for, it would help to have at least one example of a model that has them. 
Satanicpuppy's answer encouraged me to do a little more research on food service models, which I didn't even really know existed for immersion blenders - in fact, most of the manufacturers in the food services industry don't even call them "immersion blenders" or any kind of blender; instead they call them power mixers.  The information in hobodave's answer is very helpful, but I was seriously skeptical of Cook's Illustrated (ATK's) recommendation (the Kalorik) for several reasons:   It's one of the cheapest models on the market.  While price alone does not guarantee quality, it's difficult for me to believe that other consumer products are being sold at over a 500% profit margin.  To sell anything so cheaply, they must be using cheap parts. It comes with (and requires you to use) a cup.  This isn't supposed to be a requirement for a good immersion blender, and the fact that Cook's Illustrated apparently actually considered it to be a feature made me skeptical of their entire review process. Cook's Illustrated never tests for durability of these products - which is understandable given their timing - but durability is actually one of my chief concerns here, and several of the Amazon reviews seem to indicate that this particular model is less than stellar in that department.  The fact that the entire housing seems to be cheap plastic is not a good sign.   So for better or for worse, I decided not to put too much stock in a review of consumer models that (a) did not even include several of the better consumer brands (i.e. Braun), and (b) came to a conclusion that I honestly felt was simply absurd.  Instead, I started looking toward the professional brands, specifically:   Bamix is supposedly the "original inventor" of the immersion blender.  They are the "prosumer" brand and seem to have quite a good offering and get good reviews.  I love the fact that they specialize exclusively in immersion blenders and offer a 10-year warranty.  However, a few things bothered me about them:   None of their models appear to have detachable shafts.  This isn't a hard requirement, but it is far easier to clean that way. They offer 2-speed variability at best.  This is probably OK for soups but a bit problematic for emulsions where you really need to work it up gradually. Their prices seem to be just a little higher than what I would consider reasonable.  I know that you pay for quality, but given their relatively underwhelming set of features, I would have expected more for that price. Despite their 10-year warranty, I found this little gem on the USA site:     [The warranty is offered provided...] 4. That the machine has not been subject to damage, misuse, or commercial use.   Even though this isn't going to be used commercially, that last phrase sticks out like a sore thumb to me.  If it can really handle anything you throw at it then why would it matter if it's used commercially?  Waring Commercial makes the "Big Stik" and "Quik Stik" line of products.  They appear to be the entry-level food-service brand, but offer some nice features in their Big Stik line; they even offer variable-speed models in the $250 range.  But the Big Stik models are huge and really not appropriate for a home kitchen, and the Quik Stik models are rather lame (fixed shaft, two-speed) and are still monstrously heavy, weighing in at over 10 pounds.  After careful examination of their product line, I came away feeling that they had the opposite problem of Bamix; that is, they are too inexpensive for a food-service model.  They put big beefy motors in there but don't seem to pay as much attention to features or overall construction, and the weight is a huge turnoff. Dynamic, who seem to really love the colour orange, was one brand that I didn't even know existed until I started searching the inventories of various food service equipment stores.  They use the "power mixer" terminology and are moderately priced for a food-service brand.  They divide their mixers into 4 product lines, the lowest being the "Minis", and these were the ones I had my eye on.  They're not as high-powered as the Waring models, but they claim that the Minis can handle up to 1 gallon / 4 litres.  In particular I had my eye on the MiniPro, which offers a detachable shaft, multiple blades, variable speed, and weighs in at just 2.2 pounds, and widely available for $179 (although the actual list price appears to be $250).  They offer only a 1-year warranty; however, since it's a food-service product, the warranty does not have weird conditions like Bamix.  And given that this same company makes mixers for up to 50 gallons, they probably know what they're doing. Finally, there's Robot Coupe, who also sport the "power mixer" terminology.  Just one look at both the price and features of one of these and it's obvious that they are the "premium" brand.  Everything is removable on these - not just the shaft but also the bell, and you can apparently even get a whisk attachment (Dynamic makes you buy the whisk and blender products separately in the Mini range, although the Junior range has "combi" units).  Their MMP 160 VV is comparable to the MiniPro feature-wise; 220 W, 12.5k RPM, and not too heavy (shipping weight is 5 lbs, not sure what the mixer itself weighs).  It even seems easy to get spare parts and they publish diagrams for DIY-ers.  The biggest disadvantage with Robot Coupe, of course, is price.  The list price of the 160 VV is $287 although it can generally be had for $243.  Compared to the Waring and Dynamic models, that's a pretty steep increase, although if money were no object, it definitely appears to pack the biggest punch.   Of the above four brands, I think a lot comes down to personal choice, as there are trade-offs between power, features (variable speed / detachable shaft), warranty, warranty conditions, and price.  I did end up going with the Dynamic MiniPro and can safely say that it is built like a tank - but I don't want this to come across as a recommendation, seeing as how the product is a gift and I haven't actually used it myself.  I'm only including that for completeness.  Really the parts of this answer that I want to call the most attention to are the sections above describing the different brands and their offerings.  If anyone here ever feels like upgrading from some junky Cuisinart or Kitchen-Aid model, then hopefully this will serve as a useful guide.  As always, prospective buyers should do their own research, and some of the information here in terms of specific models may be localized - although I'm fairly confident that the brands themselves don't change that often, since all of these guys have been in business for 30-50 years. 