Well, depends on the budget. If you want something that's entry level but still maintains high implementation standards, consider an Alpine MRX series, such as F35 or F65. The MRX-F35 is rated at 4x60watts RMS at 4ohm. Being somewhat underrated (from past observations), in reality this amp should give you the 70watts you want. If you can afford more, the F65 should have even more power. On higher budget, Alpine PDX-4 or JL HD series should be a step up.
Another high quality amplifier is Boston Acoustics GT-475 (rated for 4x75). They used to be more expensive, but now you can find one for under $200, because the company is getting out of car audio business and some online vendors are clearing their old stock. If you want something even cheaper, see if you can find one of the discontinued MB Quart REF4.80. These have clean power and quite underrated, and will well over than the 4x80watts. These run really hot, so I wouldn't connect low impedance speakers to them.