Tax-Exempt Yields Rise But Don't Spike in 2007; Top Tax-Exempt Funds. The week following April 15 brings large outflows from money market funds, particularly Tax-Exempt ones. But yields, which normally rise dramatically, rose only several basis points this year from March 31 through yesterday. Investors should take care not to choose tax-free funds based on a temporarily high rate; check the yield once the squeeze has abated. Currently, the top-yielding (7-day as of 4/18) Tax-Exempt (and Municipal, which can hold over 20% AMT paper) funds are: 1) Lehman Bros. National Muni (3.67%); 2) Morgan Stanley Inst Liq T-E (3.63%) and Vanguard PA T-E MM; 4) Alpine Muni MM and Vanguard Tax-Exempt MM (3.62%); and 6) Federated Muni Obligations, Vanguard OH T-E MM, and Vanguard NY T-E MM (3.59%).