The SRD Card Generator is "a printable index card generator for the SRD and other OGL content." So what does that mean? Well, it's a small tool that lets you generate PDFs of things that you pick and chose from the SRD (and other OGL content). Said PDFs are formatted in such a way that they can be printed out and chopped up into index cards. So, no more buying over priced, pre printed cards. Pick what you need a la carte, print it out, and go.
Using the card generator is just about as easy as can be. Start by selecting the "Item Type" that you're looking for. Items are grouped based on a combination of the source material and what they are (spells, monsters, items, etc...). When you select the type, the list of available items will populate. Simply hilight the item(s) you want, and click the [→] button. This will copy the items into the selected pane. You can mix and match items of various types, and even select multiple copies of items. To remove items, hilight them in the selected pane and click the [←] button. Use the [↵] button to remove everything from the selected pane. When you're done selecting, just click the "Create PDF" button.
A new window will open up and load a PDF document containing your selections. You can now print the document, and it is suitable for cutting up into index cards. For the best results I recommend using paper templates (such as the kind made by Avery), and printing on them. They're usually perforated and split nicely into even cards.
This particular combination makes a nice "initiative card" for your monsters. On the upper right corner of the printout, you'll see a box containing the init modifier the creature receives followed by plenty of whitespace. What I like to do is fill in the creature's rolled initiative in the whitespace. I keep similar cards for the players (blank player templates will be perfected available before long) and likewise fill them in. When combat starts, I arrange them into the correct order by initiative. Cycling through the cards one by one tells me whose turn it is and gives me access to the stats for each monster or player right when I need them.