I use a 'Qstarz' GPS timer, model 1000ex. (about $150) It doesn't have a display so you download it to your PC. It provides really good timing plots and analysis of your laps. The software is initially a bit abstruse, but ultimately, it works pretty well. The GPS part seems to be one of the best (at 10HZ rate) and certainly has one of the best cost/benefit ratios.

Qstarz has another product, 6000LQ, which has a small display that provides predictive lap timing.  Because of how well the 1000ex works, I am tempted to try that but it costs U$500.

I also use a smartphone with RaceChrono Pro App that functions as a low cost data acquisition system. With my previous phone, the Qstarz worked really well as the GPS source, but my current phone doesn't seem to work as well. So now I use the built in GPS which is not very accurate but at least correlates with the data coming from my 'RaceDAC' low cost data acquisition system.

Sorry about the delay in replying; missed this post until recently

Hard to beat free, but if you want something that's a bit more than a lap timer, the AiM Solo is pretty great:

http://aimsports.com/products/solo/