I've just done a big batch of my own (do them every year), and use a very simple but effective recipe that works every time.
The recipe linked above is fine, but if you're used to the taste of commercial jars of pickled jalapenos then you may find it too vinegary. Jalapenos have quite a subtle taste that can be overpowered by too much vinegar, and I find that a ratio of two-thirds water to one of vinegar works really well. You're looking to make more of a brine really.
Simple Pickled Jalapeno Recipe
For Brine (I'm using cups for simplicity - standard mug of tea size, but it doesn't really matter)
water - 2 cups
white spirit vinegar - 1 cup
salt - 1tbsp (adjust to taste)
sugar - halt to 1tbsp (again, adjust to personal taste)
jalapeno - as needed - cut into thin slices (I use a mandolin for added excitement).
(You can add some dill seed and some sliced garlic if so desired, but I prefer the pure taste of the jalapenos)
NB: The amount of brine you make and the number of jalapenos required obviously depends on the size of your pickling jar(s). The above quantity of brine will easily be enough for a 2-pint jar stuffed to the brim with sliced chillies. If you're worried about not having enough brine, then simply rack it up. It's not expensive to make and any excess can be ditched if necessary.
Method
Make the brine solution by chucking the water, vinegar, salt and sugar into a pan and bringing to the boil. While it's heating up, slice your chillies.
Once the brine has come to the boil, chuck in the sliced chillies and take off the heat. Leave for 10 minutes or so (they will turn that gherkin-ish colour), and transfer to the jar(s).
Seal and allow to cool down before putting in the fridge.
Job done!