Left handed gaming mouse's (done a lot of research and testing on the subject being a lefty myself)
http://www.microsoft.com/hardware/mouseandkeyboard/productdetails.aspx?pid=004
Microsoft intellimouse 1.1 ($£10-200 higher end for customised paint jobs)
Advantages: this is the nokia 3310 of mice, 5 button mouse, big easy to find buttons on both sides, perfeclty semetrical, Low cost, optical precision (moves fast accross surfaces without loosing track) Lightweight, very durable and moddable, still used by many pro gamers.
Disadvantages: Aging hardware (plasticy) & software, only 400 dpi (moves slowly at optimal speed settings)
Optical Technology
Navigate with better speed, accuracy and reliability—the optical sensor tracks movement on nearly any surface without the hassle of clogged mouse parts.
Comfortable in Either Hand
Use your mouse with your left or right hand—ambidextrous design makes it comfortable either way.
Internet Hot Keys
With the touch of a button you can quickly access the Internet.
Additional Features:
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Scroll Wheel
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Customizable Buttons
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5 Year Warranty
http://www.virtual-hideout.net/reviews/Logitech_G3_Laser/index.shtml
Logitech g3
Advantages: Also perfectly semetrical, Fast 2000dpi, feels well built with grippy buttons 6 in total one on each side two standard mouse buttons mousewheel click and a button behind the mousewheel.
Disadvantages: can be quite difficult to find now, £20-60, the shape is not for everyone.
* Tracking Resolution: 2000dpi
* Image Processing: 6.4 megapixels/second
* Max. Acceleration: 20G
* Max. Speed: 45—65 inches/second (depending on surface)
* USB Data Format: 16 bits/axis
* USB Report Rate: 500 reports/second
* Sleep Mode: Disabled
* Dynamic Coefficient of friction - Mu (k): 0.09 (tested on wood-veneer desktop)
* Static Coefficient of friction - Mu (s): 0.15 (tested on wood-veneer desktop)
* Buttons (Left/Right): 8 million clicks
* Feet: 250 kilometers
http://www.razerzone.com/gaming-mice/razer-copperhead/
Razer Copperhead
Advantages: 2 buttons either side of the mouse & mousewheel click, fast enough dpi for most 2000 (same as g3), its glowy, symetrical design, well built rubbery feel. heavy (might be a + or - depending on your preference)
Disadvantages: Awkward tubing design that pokes out on each side obscuring the ease of pressing the side buttons (especially one ones near your ring and pinky finger). Expensive for what is essentialy a glowy but less ergenomic logitech g3. (£30-70)
* 2000dpi Razer Precision™ laser sensor
* 32KB Razer Synapse™ onboard memory
* 1000Hz Ultrapolling™ / 1ms response time
* Seven independently programmable Hyperesponse™ buttons
* On-The-Fly Sensitivity™ adjustment
* Always-On™ mode
* Zero-acoustic Ultraslick™ Teflon feet
* 16-bit ultra-wide data path
* Up to 45 inches per second and 20g of acceleration
* 7080 frames per second
* GlowPipe™ non-slip side rails
* Ergonomic ambidextrous design
* Ultra-large non-slip buttons
* Gold-plated USB connector
* Seven-foot, lightweight, non-tangle cord
* Approximate size: 130mm (length) x 66mm (width) x 41mm (height)
http://www.xsreviews.co.uk/reviews/peripherals/razer-lachesis/
Razer Lachesis
Advantages: State of the art 4000dpi lazer technology with on the fly dpi switching, symetrical left or right handed design, 9 buttons total, 2 on each side 3 on the top inclusing the mouse click and the 2 standard mouse buttons, grippy matte finish, rubbery feel, lightweight.
Disadvantages: Expensive £50-£100, Odd shape with bulky rear the seems to poke up into your palm forcing users to adopt a fingertip controll approach ( not a problem if you already do this )
* 4000dpi Razer Precision 3G Laser™ sensor
* 32KB Razer Synapse™ onboard memory
* Nine independently programmable Hyperesponse™ buttons
* 1000Hz Ultrapolling / 1ms response time
* On-The-Fly Sensitivity™ adjustment
* Variable true dpi setting adjustments in increments of 125dpi
* Always-On™ mode
* Ultra-large non-slip buttons
* 16-bit ultra-wide data path
* 60-100 inches per second*
* Ambidextrous design
* Scroll wheel with 24 individual click positions
* Zero-acoustic Ultraslick™ Teflon feet
* Gold-plated USB connector
* Seven-foot, lightweight, non-tangle cord
* Approximate size: 129mm (length) x 71mm (width) x 40mm (height)
There are other mouses on the market but these 4 are the best.