There have been a couple superb threads on various forums on this subject lately. Here's a good one:
Shimano SPD- R Pedals
You basically have the following choices:
1. standard road pedals
2. toe clips and straps -- either Shimano PD-7400 pedals (which are the classic choice) or any kind of MKS or similar cage pedal with toe clips and straps. One big advantage of the PD-7400's is that they use a standard Look drilling.
3. MKS Exa pedals -- an integrated locking mechanism in the pedal, used in conjunction with clips and straps. Not all that popular, but they do use Look drillings on the shoes.
4. Modified clipless pedals -- the most common being SPD-R pedals with a toe strap added. The thread cited above shows a number of neat ways to do this. The problem is finding the pedals, then finding shoes that have the funky SPD-R drilling.
At World Cup level, most riders are using either PD-7400's or SPD-R's. With 7400's you don't really need toe clips -- many riders don't use them either because they can't get the size clips they need or because the clip just is uncomfortable. You can figure out a routing for the straps that puts them in the right place and holds securely without the clip. Toe clips are mostly for keeping a toe strap in place so you can get your foot in and out quickly, but this is more of a road need than a track one, and with decent laminated straps you have so much stiffness you don't have to worry about the strap collapsing on you.
The alternatives are quite pricey and equally idiosyncratic, so buy a pair used and try them out at some point if you're so inclined (new PD-7400's with cleats at Business Cycles run you about $289 for the pedals plus $57 for the cleats; new SPD-R PD-7701's are getting to be $125-150 plus $35 for the fixed cleats plus $175 for compatible shoes). Except in match sprint, kilo, and team sprint, and perhaps keirin, you shouldn't have a problem unclipping anyway. Those events just aren't all that common on regular race schedules at the tracks, so until you've really raced quite a bit, I'd suggest you just use the road pedals you already know, and perhaps tighten up the tension.