just to follow up, I'd go the cassette route first - cheaper than chainrings, and may be easier for your rear derailleur to 'adapt' than the front. Of course, if this is an old bike you may want to put a new chain and chainrings on in the interest of smooth shifting and even wear. i did this as my bike is 14 years old; I swapped the original 46/36/26 triple for new rings. I wanted a 48 up front but my derailleur wouldn't have handled it well. I stuck with 46 (plenty high for my commute in city stop & go traffic), but went down to 35 and 24 rings to compliment the higher-geared cassette.

I love my new 13-23 on the mtb for pavement use. Not only do I have good chainline when using the granny ring (24x23 is plenty low; the original was 26x30 which was just overkill on the road) but my cassette has smaller jumps which are great in traffic. Y9u appreciate a big four tooth drop when you hit a steep dirt hill with loose gravel and rocks, etc. but it just isn't necessary on pavement.