Origin Live Sell modified Rega arms (will also modify your arm if needed), improvements available include a crude VTA adjustment and a structural modification, the structural mod is very good and make this version a better buy than the similarly updated Rega 600.
Ortofon Has recently restarted making some of their classic tonearms in response to the ongoing popularity of the classic SPU MC pickup line in Germany and Japan, it was getting difficult to get arms that mated with that line outside of the second hand market. Ortofon does not have info on those arms on their hompage nb., but you can get info on this dealers site. The RMA 212 i is for the SPU A range of cartridges only, it's also available in a 12" version called RMA 309 i. For the SPU G series of carts you can get the 9" RMG 212 i and the 12" RMG 309 i. All of those arms have a VTA adjustment BTW but no antiskating if I remember it correctly.
Pluto Audio This Dutch company has an interesting range of arms called 2A, 5A, 7A and 9A, and you can get more info on them here.
Pro-Ject Makes some very cost effective tonearms, some of their newer designs are especially noteworthy but it seems that they are only available separately from the players they make in some markets but not for instance in the UK or USA (Although that may change), their Model 9 is an excellent product in it's own right, cast in one piece out of aluminium and features an on the fly adjustable VTA, it is also available in slightly more complex version that has an armtube made out of carbon fibre called Model 9c there is also a variant of the 9c available that has an effective arm length of 305 mm in the form of the Model 12c which is the most cost effective 12" arm to be found out there.
Rauna They make the Cantus passive linear tracking tonearm and sell it at a remarkable price for that type of arm, only 4000 Swedish kronas including VAT, that is slightly less than £ 260 (update: the price seems to have been increased slightly when they converted into €). With shipping to the UK or anywhere else in the EU it's actually a bit less than a Rega RB600, and that has to be something of a bargain, you can also find the mounting instructions for the arm here.
Rega Makes a family of arms that all share the same basic armtube but feature different bearings etc., the cheapest model is the RB 250, it has brass components and a double sided bearing while the RB 300 sports an improved single sided bearing, the RB 600 and the RB 900. Rega introduced a new tonearm in 2002 called RB 1000, it has an armutube made out of nude aluminium that is even more rigid than previous Rega designs and features better wiring also, while it has the same bearings as the 900 those tighter tolerances . These models are extremely cost effective and thus popular amongst budget audiophiles, there has in fact grown up a small cottage industry that does nothing but provide upgrades for those arms. Expressimo make an arm lifter for Rega arms that does not interfere with the operation of the arm and thus has little effect on the sound quality, they also have a rewiring kit for the arms, a replacement weight and a VTA collar. You also have 2 options if you want to upgrade the weight on your Rega, the company itself will sell you a Tungstein weight like the one they use in their top of the line model and one of those mad Englishmen will show you how to improve the current one by using a lead-alloy. One of the main criticism of the Rega arms it the lack of an VTA adjustment, Townshend makes or made a VTA collar for Rega arms that fits beneath the arm and allows you to adjust the VTA, Michell Engineering and Galibier Design (see here)also makes a similiar devices.
RS-Labs Makes a patented type of an pivoted tonearm called the RS-A1, I cannot find a homepage for the company but the arm is reviewed here.
Scheu Makes at the least 2 arms, although meant to be fitted onto his decks they are available seperatly and in a 10" or 12" versions.
Schr÷der Tonarme Manufactures the stunning No.1 tonearm with replaceable armtubes that you can get out of carbon fibre or a few types of wood, furthermore he makes the somewhat cheaper No.2 model and the top of the line Die Referenz. The company does not appear to have a homepage but has a publicly accessible http folder that contains lots of yummy pictures in jpeg format along with textual info and manuals in microsoft word format (please note that those documents are saved in a recent version of the format so if you have an older version of Word or use another WP they may not show unless you download a viewer from Microsoft (OS/2 Worpro 1.7 opened the files but 1.6 did not)).
SME ltd. For a time in the 80's the name SME was almost synonymous with the tonarm, such was the head start that the company had on other manufacturers. They still make their classic 3009 range, the model 3009/S2 Improved is the model most like the classic SME's of the 70's with it's detachable headshell and 9,5 gram effective mass, but modern audiophiles are often more inclined towards the "3009 Series II Improved" model that is the same basic arm but has an integrated headshell minimising resonance and lowering the effective mass to 6,5 grams. (you can get counterweights for the S2 improved series if you want to use heavier pickups). The Series IIR are slightly more specialised versions of the 3009 geared toward medium and low compliance carts and transcription decks, the arms are fabricated out of steel rather than aluminium. The 3009-R has a slightly longer pivot>stylus range than normal (233.2 mm) and an effective mass of 12,7 grams. the 3010-R has a pivot>stylus length of 239,3 mm and an effective mass of 12,8 grams and finally the 3012-R has a pivot>stylus length of 308,8 mm and an effective mass of 14 grams, (those 3012-R models are ever so popular in Germany). All the Series II-R have a detachable headshell and all of the 30XX models can use the optional fluid damper.
In the mid 80's SME ltd. introduced a revolutionary new arm called the Series V, it sported a unique design made out of magnesium alloy that wherby the toneam was moulded as one piece rather than the bonded construction of their older arms. At the time the most expensive arm in the world and arguably the best, it was an immediate hit and sold by the bucket load, however despite all the qualities that arm has it was well outside of what the average consumer could pay for a tonearm so SME ltd. introduced the Series IV a couple of years later, its a simplified version of the V that has the same magnesium one piece tonarm at a considerably lower price, this model has been reviewed by TNT-Audio. The Series 300 arm is a low cost arm that is visually similar to the V but made out magnesium and is really a replacement for the old Series III line, it sports a detachable headshell and is available in three lengths, 9", 10" and 12", but it's too expensive in relation to the IV to be truly a good choise.
It's shuld be noted that the Scale Model Equipment company (yes !) also makes variants of their designs to order if you require something special, for instance you can still get the 3009 series III variant intended for use with high compliance MM pickups. The company also has a range of high end arms called Series 3500 that I have had problems getting concrete info on..
SPJ Makes a high end unipivot called Lyla Mk 2 and is made out of titanium, the Lyla is normally is shipped with their turntables but can also be had separately. Amongst other features it has an interesting on the fly VTA adjustment arrangement, more info here.