I have, currently, a Cisco Aironet 350 wifi card for my laptop, and it is doing an adequate job, but my shitty linksys router has horrible signal strenth, not to mention my desire to do some wardriving. Point being, I am in the market for a new wifi card for my Mandrake 9 system. Obviously, it has to be linux compatible, and have the ability for an external antenna to be attached without hardware modding. I have no desire to tear apart my cisco card and fuck it up beyond repair.
Any recommendations on a good card, antenna, and pigtail assembly?

It will be hard to beat your Cisco card, but for the criteria listed, I'd suggest some iteration of the Zcomax line. The XI-325 and the XI-325HP both have an antenna that "snaps" off revealing two MMCX connectors. You're more likely to see other labels: The SMC2532W-B is a rebadge of the XI-325HP, for example; the ZyXEL ZyAIR B-101, a rebadged XI-325.

I use the SMC in my AP and the B-101 in my laptop with a 5dB omni mag mount for Kismet drives.

How well do most of the omnidirectional antenna work? Im constructing a waveguide cantenna but that is obviously not going to be used for simple wardriving.

I've only used the omni to see what was out there, never for two-way communications so I can't vouch for its effectiveness other than in receive mode. That said, it picks up stuff a long way off - several blocks to 1/4 mile away.

I got this one mostly due to cost (I paid under $20 for the antenna, magnetic base and pigtail). The antenna unscrews from the base. The connectors (antenna lead-in and the antenna itself without the base) are SMA. The B-101 was about $60. I've yet to try the 200mw card in the laptop - I'm not expecting and improvement in receive in an case.