I went to the ear plug store (online) as mentioned and bought a sample pack of throw-aways (16.00 -- 40 different pairs) and a sample pack of reusable plugs (12.00 -- 16 pairs). I found a few that fit nicely, but reuseable earplugs are just that, reusable. They don't clean well and ultimately you will have to replace them. This past winter, I bought a pair of molded plugs at the IMS (bigearinc.com) and am very happy with them. They are guranteed to fit and also retain your mold so that you can have them made in case they are lost. The plugs clean well and feel very good in your ear. They are a firmer feel than the foam disposables and many of the resuable plugs, and may take some getting used to, but stick with it. They are comfortable to wear for a full session (or a solo race) and I do not even know they are there. They do a better job of noise cancelling than the disposables as well.
If you haven't used plugs before, experiment and find what works best for you and is comfortable. For me the molded plugs have made things easier.