Without further ado:
Microsoft IntelliMouse Explorer 3.0.
The IntelliMouse is famous in FPS circles. It's used by a large number of professional CS and CS:S gamers; in fact, more professional gamers use this mouse than any other mouse. This is often because they started out with it, though, and they stick with it because changing the gear they're so accustomed to as to be practically part of their muscle memory is a thoroughly bad idea.
Even so, when Microsoft released a new and updated version of the IntelliMouse a couple years back, I got excited and took one home.
It wasn't the gaming revolution of the hype machine. Oh, it was okay; the design is comfortable and it's responsive, but it's pretty big, and the side buttons are made of plastic bullshit and chips. It also has limited DPI, which was a big problem for me because I play with fairly high sensitivity, but it's not an issue for my SC-gaming friend whom I ended up donating it to. This was probably 18 months back, and unless I miss my guess he's still using it.
Main reason I didn't keep using it is because I couldn't use it with my abnormally high sensitivity. Most people should be fine with it, though.
If you like the IntelliMouse mouse design, but want a newer mouse, may I recommend:
The Razer DeathAdder.
I won't lie: This is one of the best mice I've ever owned. The design is nice. It runs at 1800 DPI. The mouse itself is of good construction. Once again, the side buttons are flimsier than I would have liked, but it's a LOT better than on the IntelliMouse. The side buttons were also poorly placed for my grip, which was disappointing but not a deal breaker. It's also pretty big, and it feels a little empty. To be honest, when I bought it I was expecting a more compact and very lightweight mouse. Instead, it was big, and fairly lightweight.
Once I grew accustomed to it, though, it was good. It was never QUITE perfect, but for the most part I had no problems with the mouse. You know, until it died.
When you buy Razer, you pretty much take a chance. Their products malfunction. Most people still have early DeathAdders that work just fine. Others have theirs die or otherwise malfunction within a year. Mine lasted about nine months before the scroll wheel went to shit, and when the mouse itself finally died another couple months later I was happy, because it meant I could replace that overly expensive piece of computer hardware in good conscience.
Still, I might have bought a new DeathAdder if I wasn't so pissed off at Razer. I would say you can't go wrong with buying a DeathAdder, but if yours dies I won't be held accountable.
Logitech MX518 Optical & G5 Laser
I'm cheating a little by lumping them together, but it's pretty much the same design with a different sensor. The original G5 Laser also had only one side button, which is total bullshit. Logitech has since "apologized" for their brilliant design decision by re-releasing the mouse as the G5 Blue which you can buy to replace the other one. Rejoice!
My G5 Laser gave me years, and when it finally went, it did so with a warning. I have not a single complaint regarding its construction, which is solid and firm. It's taller than the other mice, but not by much.
Certain design elements could have been improved, though. For example, your thumb is supposed to rest within that little grove below the side buttons. That's fine and all, but the bottom part of the mouse ends in a sharp edge for some stupid reason. If you like holding the mouse with your fingers close to the mouse pad, your thumb will be raw within the hour.
Okay, fine. The mouse wheel is noisy, and the cord is very stiff. There's your construction complaint.
The difference between optical and laser is mostly a question of mouse prediction. If you know what that is and absolutely, positively must have a mouse that doesn't have prediction (i.e. you're a hard core CS gamer), get the MX518. If it doesn't matter to you, I'd go for the laser variant.
In my opinion you can't really go wrong with either of these two. They're tried and tested.
SteelSeries Ikari Laser.
I was on the fence as to whether or not I should get this one. It comes with a hefty price tag, and I've never had a mouse be so much better than my current functional mouse that it was worth it. In the end, I held off until my DeathAdder died, upon which I decided to go back to my favoured mouse design. I used the G5 for a while, then bought the Ikari.
This thing is a beast. Construction wise, it is excellent. The main buttons are responsive, the mouse wheel is barely audible, the cord isn't too stiff, the side buttons are solid if too easy to press.
Design wise, it's a G5 on steroids, if the G5 had a rest for your ring finger. The main issue with the Ikari comes with the thumb grove, which is much too high. It feels better than the G5 (and doesn't have the sharp edge of death), but your thumb is practically touching the side buttons at all times. I accidentally pressed mouse 4 once while editing this. To remedy this, I some times press downward with my thumb on the thumb rest, but if I do this it's hard to get a grip to lift the mouse without the thumb slipping and hitting the easily pressed side keys.
It's such a shame. If it wasn't for this one gripe, I would recommend the Ikari wholeheartedly over all other mice, because everything else is made of win. I can even press the mouse wheel button without ever accidentally scrolling, which most mice have a problem with.
If you can get your literal hands on an Ikari and perhaps try it out before you purchase, I recommend doing so, because if you find you have no problems with the thumb rest it's a fantastic and lightweight mouse. You'll have to decide if it's worth the price tag, though.