The best thing I've used to check caps is an ESR meter. Electrlytic caps usually either short, or develop high internal resistance. Shorts are easy to find, but a cap with high ESR may test close to its rated capacitance. The analog ohm meter test is often inconclusive and a DMM's ohm range is totally useless for this as you've seen. There's an excellent kit available here which allows in circuit ESR testing. The first thing I do now is check all the electrolytics and replace any that are higher than normal. Now I don't have to replace a lot of good caps to make sure no marginal ones are left in. If you ever work on switching power supplies, it will pay for itself one the first repair. For small caps, a decent digital cap meter is good.
http://www.anatekcorp.com/testequipment/esr.htm