The Turion 64 X2 on Socket S is not available yet.
When it is AMD will 'catch up' to Intel in the mobile sector.
Do you require an x64 Operating System for x64 application development ?
- If no the Intel Core Duo is your best bet.
http://www.intel.com/products/processor/coreduo/index.htm
There are 25w Turion 64 MT series, single cores, available, but they still use more power than the 27w Pentium M (etc) for reasons I will not go into.
The Turion 64 ML series is actually 35w, and even worse off.
However, if you are hell bent on it, the best Turion 64 laptops are here:
http://www.hpshopping.com/cgi-bin/shopping/site_entrance.cgi?template_type=computer_store&landing=notebooks&category=hp_pavilion&aoid=1426
http://www.hpshopping.com/cgi-bin/shopping/site_entrance.cgi?template_type=computer_store&landing=notebooks&category=compaq_presario&aoid=1433
http://h10010.www1.hp.com/wwpc/us/en/sm/WF02d/321957-64295-89315.html
Toshiba and Samsung models are also quite nice.
The AMD Turion prices are so nice you can afford a 2nd, or 3rd, battery and more RAM when compared to Intel 'Centrino' platforms though.
But if you are looking to spent US$3500 you are in a tough place, because Intel Core Duo (2nd gen, Merom core) will sport both x64 and execute +63% more Instructions Per Clock cycle, aswell as being clocked +25% higher, having more cache, and being dual-core. - But that is slated for an 'around July' release. (In laymens it will have twice the performance [1.63 x 1.25] of current mobile dual-core laptops).
AMD do not have dual-core in the mobile sector yet, they are also only offering single-channel DDR1 (2.7 GB/sec usually, as they use PC2700 for power reaons). But they do have the x64 advantage as most current Intel laptops can not run an x64 OS.
The question is, do you need an x64 OS ?, and if so why do you 'really' need it ?, Having an x64 capable processor and running Win32 Kernel on it is really a waste.
I don't think the Athlon 64 Mobile (DTR) will ever get a dual-core (X2) varient added to its line, as AMD are concentrating on the Turion 64 and future Turion 64 X2 lines now.